Subject: Re: Emitting JSON to file using COPY TO

From: Masahiko Sawada <[email-masked]>
Date: Fri, 19 Jan 2024 17:09:47 +0900

On Thu, Dec 7, 2023 at 10:10 AM Joe Conway <[email-masked]> wrote:
>
> On 12/6/23 18:09, Joe Conway wrote:
> > On 12/6/23 14:47, Joe Conway wrote:
> >> On 12/6/23 13:59, Daniel Verite wrote:
> >>>     Andrew Dunstan wrote:
> >>>
> >>>> IMNSHO, we should produce either a single JSON
> >>>> document (the ARRAY case) or a series of JSON documents, one per row
> >>>> (the LINES case).
> >>>
> >>> "COPY Operations" in the doc says:
> >>>
> >>> " The backend sends a CopyOutResponse message to the frontend, followed
> >>>     by zero or more CopyData messages (always one per row), followed by
> >>>     CopyDone".
> >>>
> >>> In the ARRAY case, the first messages with the copyjsontest
> >>> regression test look like this (tshark output):
> >>>
> >>> PostgreSQL
> >>>      Type: CopyOut response
> >>>      Length: 13
> >>>      Format: Text (0)
> >>>      Columns: 3
> >>>     Format: Text (0)
> >>> PostgreSQL
> >>>      Type: Copy data
> >>>      Length: 6
> >>>      Copy data: 5b0a
> >>> PostgreSQL
> >>>      Type: Copy data
> >>>      Length: 76
> >>>      Copy data:
> >>> 207b226964223a312c226631223a226c696e652077697468205c2220696e2069743a2031…
> >>>
> >>> The first Copy data message with contents "5b0a" does not qualify
> >>> as a row of data with 3 columns as advertised in the CopyOut
> >>> message. Isn't that a problem?
> >>
> >>
> >> Is it a real problem, or just a bit of documentation change that I missed?
> >>
> >> Anything receiving this and looking for a json array should know how to
> >> assemble the data correctly despite the extra CopyData messages.
> >
> > Hmm, maybe the real problem here is that Columns do not equal "3" for
> > the json mode case -- that should really say "1" I think, because the
> > row is not represented as 3 columns but rather 1 json object.
> >
> > Does that sound correct?
> >
> > Assuming yes, there is still maybe an issue that there are two more
> > "rows" that actual output rows (the "[" and the "]"), but maybe those
> > are less likely to cause some hazard?
>
>
> The attached should fix the CopyOut response to say one column. I.e. it
> ought to look something like:
>
> PostgreSQL
>       Type: CopyOut response
>       Length: 13
>       Format: Text (0)
>       Columns: 1
>       Format: Text (0)
> PostgreSQL
>       Type: Copy data
>       Length: 6
>       Copy data: 5b0a
> PostgreSQL
>       Type: Copy data
>       Length: 76
>       Copy data: [...]
>

If I'm not missing, copyto_json.007.diff is the latest patch but it
needs to be rebased to the current HEAD. Here are random comments:

---
 if (opts_out->json_mode)
+   {
+       if (is_from)
+           ereport(ERROR,
+                   (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                    errmsg("cannot use JSON mode in COPY FROM")));
+   }
+   else if (opts_out->force_array)
+       ereport(ERROR,
+               (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                errmsg("COPY FORCE_ARRAY requires JSON mode")));

I think that flatting these two condition make the code more readable:

if (opts_out->json_mode && is_from)
ereport(ERROR, ...);

if (!opts_out->json_mode && opts_out->force_array)
ereport(ERROR, ...);

Also these checks can be moved close to other checks at the end of
ProcessCopyOptions().

---
@@ -3395,6 +3395,10 @@ copy_opt_item:
                {
                    $$ = makeDefElem("format", (Node *) makeString("csv"), @1);
                }
+           | JSON
+               {
+                   $$ = makeDefElem("format", (Node *) makeString("json"), @1);
+               }
            | HEADER_P
                {
                    $$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3427,6 +3431,10 @@ copy_opt_item:
                {
                    $$ = makeDefElem("encoding", (Node *) makeString($2), @1);
                }
+           | FORCE ARRAY
+               {
+                   $$ = makeDefElem("force_array", (Node *)
makeBoolean(true), @1);
+               }
        ;

I believe we don't need to support new options in old-style syntax.

---
@@ -3469,6 +3477,10 @@ copy_generic_opt_elem:
                {
                    $$ = makeDefElem($1, $2, @1);
                }
+           | FORMAT_LA copy_generic_opt_arg
+               {
+                   $$ = makeDefElem("format", $2, @1);
+               }
        ;

I think it's not necessary. "format" option is already handled in
copy_generic_opt_elem.

---
+/* need delimiter to start next json array element */
+static bool json_row_delim_needed = false;

I think it's cleaner to include json_row_delim_needed into CopyToStateData.

---
Splitting the patch into two patches: add json format and add
force_array option would make reviews easy.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

---

From: jian he <[email-masked]>
Date: Tue, 23 Jan 2024 13:31:00 +0800

> needs to be rebased to the current HEAD. Here are random comments:

please check the latest version.

> I think that flatting these two condition make the code more readable:

I make it two condition check

> Also these checks can be moved close to other checks at the end of
Yes. I did it, please check it.

> I think it's not necessary. "format" option is already handled in

test it, I found out this part is necessary.
because a query with WITH like `copy (select 1)  to stdout with
(format json, force_array false); ` will fail.

> I think it's cleaner to include json_row_delim_needed into CopyToStateData.
yes. I agree. So I did it.

> force_array option would make reviews easy.
done. one patch for json format, another one for force_array option.

I also made the following cases fail.
copy copytest to stdout (format csv, force_array false);
ERROR:  specify COPY FORCE_ARRAY is only allowed in JSON mode.

If copy to table then call table_scan_getnextslot no need to worry
about the Tupdesc.
however if we copy a query output as format json, we may need to consider it.

cstate->queryDesc->tupDesc is the output of Tupdesc, we can rely on this.
for copy a query result to json, I memcpy( cstate->queryDesc->tupDesc)
to the the slot's slot->tts_tupleDescriptor
so composite_to_json can use cstate->queryDesc->tupDesc to do the work.
I guess this will make it more bullet-proof.
From 214ad534d13730cba13008798c3d70f8b363436f Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Tue, 23 Jan 2024 12:26:43 +0800
Subject: [PATCH v8 2/2] Add force_array for COPY TO json fomrat.

make add open brackets and close for the whole output.
separate each json row with comma after the first row.
---
 doc/src/sgml/ref/copy.sgml         | 14 ++++++++++++++
 src/backend/commands/copy.c        | 17 +++++++++++++++++
 src/backend/commands/copyto.c      | 30 ++++++++++++++++++++++++++++++
 src/backend/parser/gram.y          |  4 ++++
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 24 ++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 10 ++++++++++
 7 files changed, 100 insertions(+)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index ccd90b61..d19332ac 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -43,6 +43,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NOT_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
+    FORCE_ARRAY [ <replaceable class="parameter">boolean</replaceable> ]
     ON_ERROR '<replaceable class="parameter">error_action</replaceable>'
     ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
 </synopsis>
@@ -379,6 +380,19 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>FORCE_ARRAY</literal></term>
+    <listitem>
+     <para>
+      Force output of square brackets as array decorations at the beginning
+      and end of output, and commas between the rows. It is allowed only in
+      <command>COPY TO</command>, and only when using
+      <literal>JSON</literal> format. The default is
+      <literal>false</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>ON_ERROR</literal></term>
     <listitem>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 5d5b733d..e15056e1 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -456,6 +456,7 @@ ProcessCopyOptions(ParseState *pstate,
 	bool		freeze_specified = false;
 	bool		header_specified = false;
 	bool		on_error_specified = false;
+	bool		force_array_specified = false;
 	ListCell   *option;
 
 	/* Support external use for option sanity checking */
@@ -610,6 +611,13 @@ ProcessCopyOptions(ParseState *pstate,
 								defel->defname),
 						 parser_errposition(pstate, defel->location)));
 		}
+		else if (strcmp(defel->defname, "force_array") == 0)
+		{
+			if (force_array_specified)
+				errorConflictingDefElem(defel, pstate);
+			force_array_specified = true;
+			opts_out->force_array = defGetBoolean(defel);
+		}
 		else if (strcmp(defel->defname, "on_error") == 0)
 		{
 			if (on_error_specified)
@@ -806,6 +814,15 @@ ProcessCopyOptions(ParseState *pstate,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot use JSON mode in COPY FROM")));
 
+	if (!opts_out->json_mode && opts_out->force_array)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("COPY FORCE_ARRAY requires JSON mode")));
+	if (!opts_out->json_mode && force_array_specified)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("specify COPY FORCE_ARRAY is only allowed in JSON mode")));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 4f55d6d5..d9245df0 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -88,6 +88,7 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+	bool		json_row_delim_needed;	/* need delimiter to start next json array element */
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -858,6 +859,16 @@ DoCopyTo(CopyToState cstate)
 
 			CopySendEndOfRow(cstate);
 		}
+
+		/*
+		 * If JSON has been requested, and FORCE_ARRAY has been specified send
+		 * the opening bracket.
+		*/
+		if (cstate->opts.json_mode && cstate->opts.force_array)
+		{
+			CopySendChar(cstate, '[');
+			CopySendEndOfRow(cstate);
+		}
 	}
 
 	if (cstate->rel)
@@ -905,6 +916,15 @@ DoCopyTo(CopyToState cstate)
 		CopySendEndOfRow(cstate);
 	}
 
+	/*
+	 * If JSON has been requested, and FORCE_ARRAY has been specified send the
+	 * closing bracket.
+	*/
+	if (cstate->opts.json_mode && cstate->opts.force_array)
+	{
+		CopySendChar(cstate, ']');
+		CopySendEndOfRow(cstate);
+	}
 	MemoryContextDelete(cstate->rowcontext);
 
 	if (fe_copy)
@@ -1006,6 +1026,16 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 		result = makeStringInfo();
 		composite_to_json(rowdata, result, false);
 
+	if (cstate->json_row_delim_needed && cstate->opts.force_array)
+	{
+		CopySendChar(cstate, ',');
+	}
+	else if (cstate->opts.force_array)
+	{
+		/* first row needs no delimiter */
+		CopySendChar(cstate, ' ');
+		cstate->json_row_delim_needed = true;
+	}
 		CopySendData(cstate, result->data, result->len);
 	}
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 702f04c3..4e13a0ab 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3468,6 +3468,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("encoding", (Node *) makeString($2), @1);
 				}
+			| FORCE ARRAY
+				{
+					$$ = makeDefElem("force_array", (Node *) makeBoolean(true), @1);
+				}
 		;
 
 /* The following exist for backward compatibility with very old versions */
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index f591b613..51656eec 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -72,6 +72,7 @@ typedef struct CopyFormatOptions
 	List	   *force_null;		/* list of column names */
 	bool		force_null_all; /* FORCE_NULL *? */
 	bool	   *force_null_flags;	/* per-column CSV FN flags */
+	bool		force_array;	/* add JSON array decorations */
 	bool		convert_selectively;	/* do selective binary conversion? */
 	CopyOnErrorChoice on_error; /* what to do when error happened */
 	List	   *convert_select; /* list of column names (can be NIL) */
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 0c5ade47..1b200b0d 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -59,6 +59,30 @@ ERROR:  cannot specify HEADER in JSON mode
 -- Error
 copy copytest from stdout (format json);
 ERROR:  cannot use JSON mode in COPY FROM
+--Error
+copy copytest to stdout (format csv, force_array false);
+ERROR:  specify COPY FORCE_ARRAY is only allowed in JSON mode
+copy copytest from stdin (format json, force_array true);
+ERROR:  cannot use JSON mode in COPY FROM
+copy copytest to stdout (format json, force_array);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array false);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 96e4f0b6..a07d27af 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -64,6 +64,16 @@ copy copytest to stdout (format json, header);
 -- Error
 copy copytest from stdout (format json);
 
+--Error
+copy copytest to stdout (format csv, force_array false);
+copy copytest from stdin (format json, force_array true);
+
+copy copytest to stdout (format json, force_array);
+
+copy copytest to stdout (format json, force_array true);
+
+copy copytest to stdout (format json, force_array false);
+
 
 -- embedded escaped characters
 create temp table copyjsontest (
-- 
2.34.1

From 0cd43bfbaeacecaffcd8167d1aab0115aa229847 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 22 Jan 2024 22:58:37 +0800
Subject: [PATCH v8 1/2] Add another COPY fomrat: json.

this format is only allowed in COPY TO operation.
---
 doc/src/sgml/ref/copy.sgml         |   5 ++
 src/backend/commands/copy.c        |  13 ++++
 src/backend/commands/copyto.c      | 121 +++++++++++++++++++----------
 src/backend/parser/gram.y          |   8 ++
 src/backend/utils/adt/json.c       |   5 +-
 src/include/commands/copy.h        |   1 +
 src/include/utils/json.h           |   2 +
 src/test/regress/expected/copy.out |  54 +++++++++++++
 src/test/regress/sql/copy.sql      |  39 ++++++++++
 9 files changed, 204 insertions(+), 44 deletions(-)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 21a5c4a0..ccd90b61 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -207,9 +207,14 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       Selects the data format to be read or written:
       <literal>text</literal>,
       <literal>csv</literal> (Comma Separated Values),
+      <literal>json</literal> (JavaScript Object Notation),
       or <literal>binary</literal>.
       The default is <literal>text</literal>.
      </para>
+     <para>
+      The <literal>json</literal> option is allowed only in
+      <command>COPY TO</command>.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index cc0786c6..5d5b733d 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -480,6 +480,8 @@ ProcessCopyOptions(ParseState *pstate,
 				 /* default format */ ;
 			else if (strcmp(fmt, "csv") == 0)
 				opts_out->csv_mode = true;
+			else if (strcmp(fmt, "json") == 0)
+				opts_out->json_mode = true;
 			else if (strcmp(fmt, "binary") == 0)
 				opts_out->binary = true;
 			else
@@ -716,6 +718,11 @@ ProcessCopyOptions(ParseState *pstate,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot specify HEADER in BINARY mode")));
 
+	if (opts_out->json_mode && opts_out->header_line)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot specify HEADER in JSON mode")));
+
 	/* Check quote */
 	if (!opts_out->csv_mode && opts_out->quote != NULL)
 		ereport(ERROR,
@@ -793,6 +800,12 @@ ProcessCopyOptions(ParseState *pstate,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("COPY FREEZE cannot be used with COPY TO")));
 
+	/* Check json format  */
+	if (opts_out->json_mode && is_from)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot use JSON mode in COPY FROM")));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index d3dc3fc8..4f55d6d5 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -28,6 +28,7 @@
 #include "executor/execdesc.h"
 #include "executor/executor.h"
 #include "executor/tuptable.h"
+#include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -37,6 +38,7 @@
 #include "rewrite/rewriteHandler.h"
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
+#include "utils/json.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/partcache.h"
@@ -146,9 +148,20 @@ SendCopyBegin(CopyToState cstate)
 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
 	pq_sendbyte(&buf, format);	/* overall format */
-	pq_sendint16(&buf, natts);
-	for (i = 0; i < natts; i++)
-		pq_sendint16(&buf, format); /* per-column formats */
+	if (!cstate->opts.json_mode)
+	{
+		pq_sendint16(&buf, natts);
+		for (i = 0; i < natts; i++)
+			pq_sendint16(&buf, format); /* per-column formats */
+	}
+	else
+	{
+		/*
+		 * JSON mode is always one non-binary column
+		 */
+		pq_sendint16(&buf, 1);
+		pq_sendint16(&buf, 0);
+	}
 	pq_endmessage(&buf);
 	cstate->copy_dest = COPY_FRONTEND;
 }
@@ -906,11 +919,7 @@ DoCopyTo(CopyToState cstate)
 static void
 CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 {
-	bool		need_delim = false;
-	FmgrInfo   *out_functions = cstate->out_functions;
 	MemoryContext oldcontext;
-	ListCell   *cur;
-	char	   *string;
 
 	MemoryContextReset(cstate->rowcontext);
 	oldcontext = MemoryContextSwitchTo(cstate->rowcontext);
@@ -921,54 +930,84 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 		CopySendInt16(cstate, list_length(cstate->attnumlist));
 	}
 
-	/* Make sure the tuple is fully deconstructed */
-	slot_getallattrs(slot);
-
-	foreach(cur, cstate->attnumlist)
+	if (!cstate->opts.json_mode)
 	{
-		int			attnum = lfirst_int(cur);
-		Datum		value = slot->tts_values[attnum - 1];
-		bool		isnull = slot->tts_isnull[attnum - 1];
+		bool		need_delim = false;
+		FmgrInfo   *out_functions = cstate->out_functions;
+		ListCell   *cur;
+		char	   *string;
 
-		if (!cstate->opts.binary)
-		{
-			if (need_delim)
-				CopySendChar(cstate, cstate->opts.delim[0]);
-			need_delim = true;
-		}
+		/* Make sure the tuple is fully deconstructed */
+		slot_getallattrs(slot);
 
-		if (isnull)
-		{
-			if (!cstate->opts.binary)
-				CopySendString(cstate, cstate->opts.null_print_client);
-			else
-				CopySendInt32(cstate, -1);
-		}
-		else
+		foreach(cur, cstate->attnumlist)
 		{
+			int			attnum = lfirst_int(cur);
+			Datum		value = slot->tts_values[attnum - 1];
+			bool		isnull = slot->tts_isnull[attnum - 1];
+
 			if (!cstate->opts.binary)
 			{
-				string = OutputFunctionCall(&out_functions[attnum - 1],
-											value);
-				if (cstate->opts.csv_mode)
-					CopyAttributeOutCSV(cstate, string,
-										cstate->opts.force_quote_flags[attnum - 1],
-										list_length(cstate->attnumlist) == 1);
+				if (need_delim)
+					CopySendChar(cstate, cstate->opts.delim[0]);
+				need_delim = true;
+			}
+
+			if (isnull)
+			{
+				if (!cstate->opts.binary)
+					CopySendString(cstate, cstate->opts.null_print_client);
 				else
-					CopyAttributeOutText(cstate, string);
+					CopySendInt32(cstate, -1);
 			}
 			else
 			{
-				bytea	   *outputbytes;
+				if (!cstate->opts.binary)
+				{
+					string = OutputFunctionCall(&out_functions[attnum - 1],
+												value);
+					if (cstate->opts.csv_mode)
+						CopyAttributeOutCSV(cstate, string,
+											cstate->opts.force_quote_flags[attnum - 1],
+											list_length(cstate->attnumlist) == 1);
+					else
+						CopyAttributeOutText(cstate, string);
+				}
+				else
+				{
+					bytea	   *outputbytes;
 
-				outputbytes = SendFunctionCall(&out_functions[attnum - 1],
-											   value);
-				CopySendInt32(cstate, VARSIZE(outputbytes) - VARHDRSZ);
-				CopySendData(cstate, VARDATA(outputbytes),
-							 VARSIZE(outputbytes) - VARHDRSZ);
+					outputbytes = SendFunctionCall(&out_functions[attnum - 1],
+												   value);
+					CopySendInt32(cstate, VARSIZE(outputbytes) - VARHDRSZ);
+					CopySendData(cstate, VARDATA(outputbytes),
+								 VARSIZE(outputbytes) - VARHDRSZ);
+				}
 			}
 		}
 	}
+	else
+	{
+		Datum		rowdata;
+		StringInfo	result;
+
+		if(!cstate->rel)
+		{
+			for (int i = 0; i < slot->tts_tupleDescriptor->natts; i++)
+			{
+				/* Flat-copy the attribute array */
+				memcpy(TupleDescAttr(slot->tts_tupleDescriptor, i),
+				TupleDescAttr(cstate->queryDesc->tupDesc, i),
+								1 * sizeof(FormData_pg_attribute));
+			}
+			BlessTupleDesc(slot->tts_tupleDescriptor);
+		}
+		rowdata = ExecFetchSlotHeapTupleDatum(slot);
+		result = makeStringInfo();
+		composite_to_json(rowdata, result, false);
+
+		CopySendData(cstate, result->data, result->len);
+	}
 
 	CopySendEndOfRow(cstate);
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 3460fea5..702f04c3 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3424,6 +3424,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("format", (Node *) makeString("csv"), @1);
 				}
+			| JSON
+				{
+					$$ = makeDefElem("format", (Node *) makeString("json"), @1);
+				}
 			| HEADER_P
 				{
 					$$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3506,6 +3510,10 @@ copy_generic_opt_elem:
 				{
 					$$ = makeDefElem($1, $2, @1);
 				}
+			| FORMAT_LA copy_generic_opt_arg
+			{
+				$$ = makeDefElem("format", $2, @1);
+			}
 		;
 
 copy_generic_opt_arg:
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index d719a61f..fabd4e61 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -83,8 +83,6 @@ typedef struct JsonAggState
 	JsonUniqueBuilderState unique_check;
 } JsonAggState;
 
-static void composite_to_json(Datum composite, StringInfo result,
-							  bool use_line_feeds);
 static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
 							  Datum *vals, bool *nulls, int *valcount,
 							  JsonTypeCategory tcategory, Oid outfuncoid,
@@ -507,8 +505,9 @@ array_to_json_internal(Datum array, StringInfo result, bool use_line_feeds)
 
 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index b3da3cb0..f591b613 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -53,6 +53,7 @@ typedef struct CopyFormatOptions
 	bool		binary;			/* binary format? */
 	bool		freeze;			/* freeze rows on loading? */
 	bool		csv_mode;		/* Comma Separated Value format? */
+	bool		json_mode;		/* JSON format? */
 	CopyHeaderChoice header_line;	/* header line? */
 	char	   *null_print;		/* NULL marker string (server encoding!) */
 	int			null_print_len; /* length of same */
diff --git a/src/include/utils/json.h b/src/include/utils/json.h
index 6d7f1b38..d5631171 100644
--- a/src/include/utils/json.h
+++ b/src/include/utils/json.h
@@ -17,6 +17,8 @@
 #include "lib/stringinfo.h"
 
 /* functions in json.c */
+extern void composite_to_json(Datum composite, StringInfo result,
+							  bool use_line_feeds);
 extern void escape_json(StringInfo buf, const char *str);
 extern char *JsonEncodeDateTime(char *buf, Datum value, Oid typid,
 								const int *tzp);
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index b48365ec..0c5ade47 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -42,6 +42,60 @@ copy copytest3 to stdout csv header;
 c1,"col with , comma","col with "" quote"
 1,a,1
 2,b,2
+--- test copying in JSON mode with various styles
+copy copytest to stdout json;
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+copy copytest to stdout (format json);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- Error
+copy copytest to stdout (format json, header);
+ERROR:  cannot specify HEADER in JSON mode
+-- Error
+copy copytest from stdout (format json);
+ERROR:  cannot use JSON mode in COPY FROM
+-- embedded escaped characters
+create temp table copyjsontest (
+    id bigserial,
+    f1 text,
+    f2 timestamptz);
+insert into copyjsontest
+  select g.i,
+         CASE WHEN g.i % 2 = 0 THEN
+           'line with '' in it: ' || g.i::text
+         ELSE
+           'line with " in it: ' || g.i::text
+         END,
+         'Mon Feb 10 17:32:01 1997 PST'
+  from generate_series(1,5) as g(i);
+insert into copyjsontest (f1) values
+(E'aaa\"bbb'::text),
+(E'aaa\\bbb'::text),
+(E'aaa\/bbb'::text),
+(E'aaa\bbbb'::text),
+(E'aaa\fbbb'::text),
+(E'aaa\nbbb'::text),
+(E'aaa\rbbb'::text),
+(E'aaa\tbbb'::text);
+copy copyjsontest to stdout json;
+{"id":1,"f1":"line with \" in it: 1","f2":"1997-02-10T17:32:01-08:00"}
+{"id":2,"f1":"line with ' in it: 2","f2":"1997-02-10T17:32:01-08:00"}
+{"id":3,"f1":"line with \" in it: 3","f2":"1997-02-10T17:32:01-08:00"}
+{"id":4,"f1":"line with ' in it: 4","f2":"1997-02-10T17:32:01-08:00"}
+{"id":5,"f1":"line with \" in it: 5","f2":"1997-02-10T17:32:01-08:00"}
+{"id":1,"f1":"aaa\"bbb","f2":null}
+{"id":2,"f1":"aaa\\bbb","f2":null}
+{"id":3,"f1":"aaa/bbb","f2":null}
+{"id":4,"f1":"aaa\bbbb","f2":null}
+{"id":5,"f1":"aaa\fbbb","f2":null}
+{"id":6,"f1":"aaa\nbbb","f2":null}
+{"id":7,"f1":"aaa\rbbb","f2":null}
+{"id":8,"f1":"aaa\tbbb","f2":null}
 create temp table copytest4 (
 	c1 int,
 	"colname with tab: 	" text);
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 43d2e906..96e4f0b6 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -54,6 +54,45 @@ this is just a line full of junk that would error out if parsed
 
 copy copytest3 to stdout csv header;
 
+--- test copying in JSON mode with various styles
+copy copytest to stdout json;
+
+copy copytest to stdout (format json);
+
+-- Error
+copy copytest to stdout (format json, header);
+-- Error
+copy copytest from stdout (format json);
+
+
+-- embedded escaped characters
+create temp table copyjsontest (
+    id bigserial,
+    f1 text,
+    f2 timestamptz);
+
+insert into copyjsontest
+  select g.i,
+         CASE WHEN g.i % 2 = 0 THEN
+           'line with '' in it: ' || g.i::text
+         ELSE
+           'line with " in it: ' || g.i::text
+         END,
+         'Mon Feb 10 17:32:01 1997 PST'
+  from generate_series(1,5) as g(i);
+
+insert into copyjsontest (f1) values
+(E'aaa\"bbb'::text),
+(E'aaa\\bbb'::text),
+(E'aaa\/bbb'::text),
+(E'aaa\bbbb'::text),
+(E'aaa\fbbb'::text),
+(E'aaa\nbbb'::text),
+(E'aaa\rbbb'::text),
+(E'aaa\tbbb'::text);
+
+copy copyjsontest to stdout json;
+
 create temp table copytest4 (
 	c1 int,
 	"colname with tab: 	" text);
-- 
2.34.1

---

From: Junwang Zhao <[email-masked]>
Date: Sat, 27 Jan 2024 13:55:23 +0800

Hi hackers,

Kou-san(CCed) has been working on *Make COPY format extendable[1]*, so
I think making *copy to json* based on that work might be the right direction.

I write an extension for that purpose, and here is the patch set together
with Kou-san's *extendable copy format* implementation:

0001-0009 is the implementation of extendable copy format
00010 is the pg_copy_json extension

I also created a PR[2] if anybody likes the github review style.

The *extendable copy format* feature is still being developed, I post this
email in case the patch set in this thread is committed without knowing
the *extendable copy format* feature.

I'd like to hear your opinions.

[1]: https://www.postgresql.org/message-id/20240124.144936.67229716500876806.kou%40clear-code.com
[2]: https://github.com/zhjwpku/postgres/pull/2/files

-- 
Regards
Junwang Zhao

---

From: vignesh C <[email-masked]>
Date: Wed, 31 Jan 2024 15:19:51 +0530

> I'd like to hear your opinions.

CFBot shows that one of the test is failing as in [1]:
[05:46:41.678] /bin/sh: 1: cannot open
/tmp/cirrus-ci-build/contrib/pg_copy_json/sql/test_copy_format.sql: No
such file
[05:46:41.678] diff:
/tmp/cirrus-ci-build/contrib/pg_copy_json/expected/test_copy_format.out:
No such file or directory
[05:46:41.678] diff:
/tmp/cirrus-ci-build/contrib/pg_copy_json/results/test_copy_format.out:
No such file or directory
[05:46:41.678] # diff command failed with status 512: diff
"/tmp/cirrus-ci-build/contrib/pg_copy_json/expected/test_copy_format.out"
"/tmp/cirrus-ci-build/contrib/pg_copy_json/results/test_copy_format.out"
> "/tmp/cirrus-ci-build/contrib/pg_copy_json/results/test_copy_format.out.diff"
[05:46:41.678] Bail out!make[2]: *** [../../src/makefiles/pgxs.mk:454:
check] Error 2
[05:46:41.679] make[1]: *** [Makefile:96: check-pg_copy_json-recurse] Error 2
[05:46:41.679] make: *** [GNUmakefile:71: check-world-contrib-recurse] Error 2

Please post an updated version for the same.

[1] - https://cirrus-ci.com/task/5322439115145216

Regards,
Vignesh

---

From: Junwang Zhao <[email-masked]>
Date: Wed, 31 Jan 2024 17:58:00 +0800

Hi Vignesh,

> Please post an updated version for the same.

Thanks for the reminder, the patch set I posted is not for commit but
for further discussion.

I will post more information about the *extendable copy* feature
when it's about to be committed.

-- 
Regards
Junwang Zhao

---

From: Alvaro Herrera <[email-masked]>
Date: Wed, 31 Jan 2024 14:26:28 +0100

> (format json, force_array false); ` will fail.

Right, because "FORMAT JSON" is turned into FORMAT_LA JSON by parser.c
(see base_yylex there).  I'm not really sure but I think it might be
better to make it "| FORMAT_LA JSON" instead of invoking the whole
copy_generic_opt_arg syntax.  Not because of performance, but just
because it's much clearer what's going on.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/

---

From: jian he <[email-masked]>
Date: Mon, 27 Jan 2025 16:16:26 +0800

hi.

There are two ways we can use to represent the new copy format: json.
1.
typedef struct CopyFormatOptions
{
    bool        binary;            /* binary format? */
    bool        freeze;            /* freeze rows on loading? */
    bool        csv_mode;        /* Comma Separated Value format? */
    bool        json_mode;        /* JSON format? */
    ...
}

2.
typedef struct CopyFormatOptions
{
    CopyFormat    format;            /* format of the COPY operation */
    .....
}

typedef enum CopyFormat
{
    COPY_FORMAT_TEXT = 0,
    COPY_FORMAT_BINARY,
    COPY_FORMAT_CSV,
    COPY_FORMAT_JSON,
} CopyFormat;

both the sizeof(cstate->opts) (CopyToStateData.CopyFormatOptions) is 184.
so the struct size will not influence the performance.

I also did some benchmarks when using CopyFormat.
the following are the benchmarks info:
-------------------------------------------------------------------------------------------------------
create unlogged table t as select g from generate_series(1, 1_000_000) g;

build_type=release patch:
copy t to '/dev/null' json \watch i=0.1 c=10
last execution Time: 108.741 ms

copy t to '/dev/null' (format text)  \watch i=0.1 c=10
last execution Time: 42.600 ms

build_type=release master:
copy t to '/dev/null' (format text)  \watch i=0.1 c=10
last execution Time Time: 42.948 ms

---------------------------------------------------------
so a new version is attached, using the struct CopyFormatOptions.

changes mainly in CopyOneRowTo.
now it is:
""""
        if(!cstate->rel)
        {
            memcpy(TupleDescAttr(slot->tts_tupleDescriptor, 0),
                   TupleDescAttr(cstate->queryDesc->tupDesc, 0),
                   cstate->queryDesc->tupDesc->natts *
sizeof(FormData_pg_attribute));
            for (int i = 0; i < cstate->queryDesc->tupDesc->natts; i++)
                populate_compact_attribute(slot->tts_tupleDescriptor, i);
            BlessTupleDesc(slot->tts_tupleDescriptor);
        }
""""
reasoning for change:
for composite_to_json to construct json key, we only need
FormData_pg_attribute.attname
but code path
composite_to_json->fastgetattr->TupleDescCompactAttr->verify_compact_attribute
means we also need to call populate_compact_attribute to populate
other attributes.

v14-0001-Introduce-CopyFormat-and-replace-csv_mode-and-bi.patch,
author is by Joel Jacobson.
As I mentioned in above,
replacing 3 bool fields by an enum didn't change the struct CopyFormatOptions.
but consolidated 3 bool fields into one enum to make code more lean.
I think the refactoring (v14-0001) is worth it.
From 38fe90d00746b7441faef4bdc392090aea1b9ee3 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 27 Jan 2025 16:05:37 +0800
Subject: [PATCH v14 3/3] Add option force_array for COPY JSON FORMAT

force_array option can only be used in COPY TO with JSON format.
it make the output json output behave like json array type.

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 14 ++++++++++++++
 src/backend/commands/copy.c        | 13 +++++++++++++
 src/backend/commands/copyto.c      | 28 ++++++++++++++++++++++++++++
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 23 +++++++++++++++++++++++
 src/test/regress/sql/copy.sql      |  9 +++++++++
 7 files changed, 89 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 5bf0f38d90..50cebec0ce 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -43,6 +43,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NOT_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
+    FORCE_ARRAY [ <replaceable class="parameter">boolean</replaceable> ]
     ON_ERROR <replaceable class="parameter">error_action</replaceable>
     REJECT_LIMIT <replaceable class="parameter">maxerror</replaceable>
     ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
@@ -392,6 +393,19 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>FORCE_ARRAY</literal></term>
+    <listitem>
+     <para>
+      Force output of square brackets as array decorations at the beginning
+      and end of output, and commas between the rows. It is allowed only in
+      <command>COPY TO</command>, and only when using
+      <literal>JSON</literal> format. The default is
+      <literal>false</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>ON_ERROR</literal></term>
     <listitem>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index c0234d22e5..2dbbd4007e 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -504,6 +504,7 @@ ProcessCopyOptions(ParseState *pstate,
 	bool		on_error_specified = false;
 	bool		log_verbosity_specified = false;
 	bool		reject_limit_specified = false;
+	bool		force_array_specified = false;
 	ListCell   *option;
 
 	/* Support external use for option sanity checking */
@@ -658,6 +659,13 @@ ProcessCopyOptions(ParseState *pstate,
 								defel->defname),
 						 parser_errposition(pstate, defel->location)));
 		}
+		else if (strcmp(defel->defname, "force_array") == 0)
+		{
+			if (force_array_specified)
+				errorConflictingDefElem(defel, pstate);
+			force_array_specified = true;
+			opts_out->force_array = defGetBoolean(defel);
+		}
 		else if (strcmp(defel->defname, "on_error") == 0)
 		{
 			if (on_error_specified)
@@ -907,6 +915,11 @@ ProcessCopyOptions(ParseState *pstate,
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				errmsg("COPY json mode cannot be used with %s", "COPY FROM"));
 
+	if (opts_out->format != COPY_FORMAT_JSON && opts_out->force_array)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s can only used with JSON mode", "FORCE_ARRAY"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index d5d1bc4ec9..764ed4766d 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -81,6 +81,7 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+	bool		json_row_delim_needed;	/* need delimiter to start next json array element */
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -858,6 +859,15 @@ DoCopyTo(CopyToState cstate)
 
 			CopySendEndOfRow(cstate);
 		}
+		/*
+		 * If JSON has been requested, and FORCE_ARRAY has been specified then
+		 * send the opening bracket.
+		*/
+		if (cstate->opts.format == COPY_FORMAT_JSON && cstate->opts.force_array)
+		{
+			CopySendChar(cstate, '[');
+			CopySendEndOfRow(cstate);
+		}
 	}
 
 	if (cstate->rel)
@@ -905,6 +915,15 @@ DoCopyTo(CopyToState cstate)
 		CopySendEndOfRow(cstate);
 	}
 
+	/*
+	 * If JSON has been requested, and FORCE_ARRAY has been specified then
+	 * send the closing bracket.
+	*/
+	if (cstate->opts.format == COPY_FORMAT_JSON && cstate->opts.force_array)
+	{
+		CopySendChar(cstate, ']');
+		CopySendEndOfRow(cstate);
+	}
 	MemoryContextDelete(cstate->rowcontext);
 
 	if (fe_copy)
@@ -1008,6 +1027,15 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 		result = makeStringInfo();
 		composite_to_json(rowdata, result, false);

diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 5fb5cb2daa..02d0d4e3cf 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3249,7 +3249,7 @@ match_previous_words(int pattern_id,
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "("))
 		COMPLETE_WITH("FORMAT", "FREEZE", "DELIMITER", "NULL",
 					  "HEADER", "QUOTE", "ESCAPE", "FORCE_QUOTE",
-					  "FORCE_NOT_NULL", "FORCE_NULL", "ENCODING", "DEFAULT",
+					  "FORCE_NOT_NULL", "FORCE_NULL", "FORCE_ARRAY", "ENCODING", "DEFAULT",
 					  "ON_ERROR", "LOG_VERBOSITY");
 
 	/* Complete COPY <sth> FROM|TO filename WITH (FORMAT */
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 07fcc2bc9a..466ab76dac 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -92,6 +92,7 @@ typedef struct CopyFormatOptions
 	List	   *force_null;		/* list of column names */
 	bool		force_null_all; /* FORCE_NULL *? */
 	bool	   *force_null_flags;	/* per-column CSV FN flags */
+	bool		force_array;	/* add JSON array decorations */
 	bool		convert_selectively;	/* do selective binary conversion? */
 	CopyOnErrorChoice on_error; /* what to do when error happened */
 	CopyLogVerbosityChoice log_verbosity;	/* verbosity of logged messages */
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index b4479bc72a..ffee7bff00 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -110,6 +110,29 @@ LINE 1: copy copytest to stdout (format json, on_error ignore);
 copy copytest from stdin(format json);
 ERROR:  COPY json mode cannot be used with COPY FROM
 -- all of the above should yield error
+--Error
+copy copytest to stdout (format csv, force_array true);
+ERROR:  COPY FORCE_ARRAY can only used with JSON mode
+--ok
+copy copytest to stdout (format json, force_array);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array false);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 054fce95cb..7a175ca76a 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -101,6 +101,15 @@ copy copytest to stdout (format json, on_error ignore);
 copy copytest from stdin(format json);
 -- all of the above should yield error
 
+--Error
+copy copytest to stdout (format csv, force_array true);
+
+--ok

From e42e0696f6362fc8aba01ef1c546c4224aaf65c1 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 27 Jan 2025 15:05:48 +0800
Subject: [PATCH v14 2/3] introduce json format for COPY TO

json format is only allowed in COPY TO operation.
also cannot be used with {header, default, null, delimiter} options and many other options.
fully tested on src/test/regress/sql/copy.sql.

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 13 ++++--
 src/backend/commands/copy.c        | 29 ++++++++++++
 src/backend/commands/copyto.c      | 51 ++++++++++++++++++--
 src/backend/parser/gram.y          |  8 ++++
 src/backend/utils/adt/json.c       |  5 +-
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/include/utils/json.h           |  2 +
 src/test/regress/expected/copy.out | 74 ++++++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 47 +++++++++++++++++++
 10 files changed, 219 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 8394402f09..5bf0f38d90 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -219,10 +219,15 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       Selects the data format to be read or written:
       <literal>text</literal>,
       <literal>csv</literal> (Comma Separated Values),
+      <literal>json</literal> (JavaScript Object Notation),
       or <literal>binary</literal>.
       The default is <literal>text</literal>.
       See <xref linkend="sql-copy-file-formats"/> below for details.
      </para>
+     <para>
+      The <literal>json</literal> option is allowed only in
+      <command>COPY TO</command>.
+     </para>
     </listitem>
    </varlistentry>
 
@@ -257,7 +262,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       (line) of the file.  The default is a tab character in text format,
       a comma in <literal>CSV</literal> format.
       This must be a single one-byte character.
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
@@ -271,7 +276,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       string in <literal>CSV</literal> format. You might prefer an
       empty string even in text format for cases where you don't want to
       distinguish nulls from empty strings.
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
      </para>
 
      <note>
@@ -294,7 +299,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       is found in the input file, the default value of the corresponding column
       will be used.
       This option is allowed only in <command>COPY FROM</command>, and only when
-      not using <literal>binary</literal> format.
+      not using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
@@ -310,7 +315,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       If this option is set to <literal>MATCH</literal>, the number and names
       of the columns in the header line must match the actual column names of
       the table, in order;  otherwise an error is raised.
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
       The <literal>MATCH</literal> option is only valid for <command>COPY
       FROM</command> commands.
      </para>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index e7e7815853..c0234d22e5 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -530,6 +530,8 @@ ProcessCopyOptions(ParseState *pstate,
 				opts_out->format = COPY_FORMAT_CSV;
 			else if (strcmp(fmt, "binary") == 0)
 				opts_out->format = COPY_FORMAT_BINARY;
+			else if (strcmp(fmt, "json") == 0)
+				opts_out->format = COPY_FORMAT_JSON;
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -695,16 +697,32 @@ ProcessCopyOptions(ParseState *pstate,
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("cannot specify %s in BINARY mode", "DELIMITER")));
 
+	if (opts_out->format == COPY_FORMAT_JSON && opts_out->delim)
+		ereport(ERROR,
+				errcode(ERRCODE_SYNTAX_ERROR),
+		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
+				errmsg("cannot specify %s in JSON mode", "DELIMITER"));
+
 	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->null_print)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("cannot specify %s in BINARY mode", "NULL")));
 
+	if (opts_out->format == COPY_FORMAT_JSON && opts_out->null_print)
+		ereport(ERROR,
+				errcode(ERRCODE_SYNTAX_ERROR),
+				errmsg("cannot specify %s in JSON mode", "NULL"));
+
 	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->default_print)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("cannot specify %s in BINARY mode", "DEFAULT")));
 
+	if (opts_out->format == COPY_FORMAT_JSON && opts_out->default_print)
+		ereport(ERROR,
+				errcode(ERRCODE_SYNTAX_ERROR),
+				errmsg("cannot specify %s in JSON mode", "DEFAULT"));
+
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
 		opts_out->delim = opts_out->format == COPY_FORMAT_CSV ? "," : "\t";
@@ -775,6 +793,11 @@ ProcessCopyOptions(ParseState *pstate,
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("cannot specify %s in BINARY mode", "HEADER")));
 
+	if (opts_out->format == COPY_FORMAT_JSON && opts_out->header_line)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("cannot specify %s in JSON mode", "HEADER"));
+
 	/* Check quote */
 	if (opts_out->format != COPY_FORMAT_CSV && opts_out->quote != NULL)
 		ereport(ERROR,
@@ -878,6 +901,12 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY %s cannot be used with %s", "FREEZE",
 						"COPY TO")));
 
+	/* Check json format  */
+	if (opts_out->format == COPY_FORMAT_JSON && is_from)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY json mode cannot be used with %s", "COPY FROM"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index ea90af28a9..d5d1bc4ec9 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -24,6 +24,7 @@
 #include "executor/execdesc.h"
 #include "executor/executor.h"
 #include "executor/tuptable.h"
+#include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -31,6 +32,7 @@
 #include "pgstat.h"
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
+#include "utils/json.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -139,9 +141,20 @@ SendCopyBegin(CopyToState cstate)
 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
 	pq_sendbyte(&buf, format);	/* overall format */
-	pq_sendint16(&buf, natts);
-	for (i = 0; i < natts; i++)
-		pq_sendint16(&buf, format); /* per-column formats */
+	if (cstate->opts.format != COPY_FORMAT_JSON)
+	{
+		pq_sendint16(&buf, natts);
+		for (i = 0; i < natts; i++)
+			pq_sendint16(&buf, format); /* per-column formats */
+	}
+	else
+	{
+		/*
+		 * JSON format is always one non-binary column
+		 */
+		pq_sendint16(&buf, 1);
+		pq_sendint16(&buf, 0);
+	}
 	pq_endmessage(&buf);
 	cstate->copy_dest = COPY_FRONTEND;
 }
@@ -921,7 +934,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	/* Make sure the tuple is fully deconstructed */
 	slot_getallattrs(slot);
 
-	if (cstate->opts.format != COPY_FORMAT_BINARY)
+	if (cstate->opts.format == COPY_FORMAT_TEXT || cstate->opts.format == COPY_FORMAT_CSV)
 	{
 		bool		need_delim = false;
 
@@ -949,7 +962,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 			}
 		}
 	}
-	else
+	else if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		foreach_int(attnum, cstate->attnumlist)
 		{
@@ -969,6 +982,34 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 			}
 		}
 	}
+	else
+	{
+		Datum		rowdata;
+		StringInfo	result;
+
+		/*
+		 * if COPY TO source data is from a query, not a plain table, then we
+		 * need copy CopyToState->TupleDesc to slot->tts_tupleDescriptor.
+		 * because the slot's TupleDesc->attrs may change during query
+		 * execution.
+		*/
+		if(!cstate->rel)
+		{
+			memcpy(TupleDescAttr(slot->tts_tupleDescriptor, 0),
+				   TupleDescAttr(cstate->queryDesc->tupDesc, 0),
+				   cstate->queryDesc->tupDesc->natts * sizeof(FormData_pg_attribute));
+
+			for (int i = 0; i < cstate->queryDesc->tupDesc->natts; i++)
+				populate_compact_attribute(slot->tts_tupleDescriptor, i);
+
+			BlessTupleDesc(slot->tts_tupleDescriptor);
+		}
+		rowdata = ExecFetchSlotHeapTupleDatum(slot);
+		result = makeStringInfo();
+		composite_to_json(rowdata, result, false);
+
+		CopySendData(cstate, result->data, result->len);
+	}

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index d7f9c00c40..cfcb200b6e 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3465,6 +3465,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("format", (Node *) makeString("csv"), @1);
 				}
+			| JSON
+				{
+					$$ = makeDefElem("format", (Node *) makeString("json"), @1);
+				}
 			| HEADER_P
 				{
 					$$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3547,6 +3551,10 @@ copy_generic_opt_elem:
 				{
 					$$ = makeDefElem($1, $2, @1);
 				}
+			| FORMAT_LA copy_generic_opt_arg
+			{
+				$$ = makeDefElem("format", $2, @1);
+			}
 		;
 
 copy_generic_opt_arg:
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 51452755f5..bf69347fa9 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -85,8 +85,6 @@ typedef struct JsonAggState
 	JsonUniqueBuilderState unique_check;
 } JsonAggState;
 
@@ -516,8 +514,9 @@ array_to_json_internal(Datum array, StringInfo result, bool use_line_feeds)
 
 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 81cbf10aa2..5fb5cb2daa 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3254,7 +3254,7 @@ match_previous_words(int pattern_id,
 
 	/* Complete COPY <sth> FROM|TO filename WITH (FORMAT */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "(", "FORMAT"))
-		COMPLETE_WITH("binary", "csv", "text");
+		COMPLETE_WITH("binary", "csv", "text", "json");
 
 	/* Complete COPY <sth> FROM filename WITH (ON_ERROR */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "(", "ON_ERROR"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 7a1ee65601..07fcc2bc9a 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -59,6 +59,7 @@ typedef enum CopyFormat
 	COPY_FORMAT_TEXT = 0,
 	COPY_FORMAT_BINARY,
 	COPY_FORMAT_CSV,
+	COPY_FORMAT_JSON,
 } CopyFormat;
 
 /*
index 49bbda7ac0..1fa8e2ce8e 100644
 
 /* functions in json.c */
+extern void composite_to_json(Datum composite, StringInfo result,
+							  bool use_line_feeds);
 extern void escape_json(StringInfo buf, const char *str);
 extern void escape_json_with_len(StringInfo buf, const char *str, int len);
 extern void escape_json_text(StringInfo buf, const text *txt);
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index f554d42c84..b4479bc72a 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -73,6 +73,80 @@ copy copytest3 to stdout csv header;
 c1,"col with , comma","col with "" quote"
 1,a,1
 2,b,2
+--- test copying in JSON mode with various styles
+copy copytest to stdout json;
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+copy copytest to stdout (format json);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- all of the following should yield error
+copy copytest to stdout (format json, delimiter '|');
+ERROR:  cannot specify DELIMITER in JSON mode
+copy copytest to stdout (format json, null '\N');
+ERROR:  cannot specify NULL in JSON mode
+copy copytest to stdout (format json, default '|');
+ERROR:  cannot specify DEFAULT in JSON mode
+copy copytest to stdout (format json, header);
+ERROR:  cannot specify HEADER in JSON mode
+copy copytest to stdout (format json, quote '"');
+ERROR:  COPY QUOTE requires CSV mode
+copy copytest to stdout (format json, escape '"');
+ERROR:  COPY ESCAPE requires CSV mode
+copy copytest to stdout (format json, force_quote *);
+ERROR:  COPY FORCE_QUOTE requires CSV mode
+copy copytest to stdout (format json, force_not_null *);
+ERROR:  COPY FORCE_NOT_NULL requires CSV mode
+copy copytest to stdout (format json, force_null *);
+ERROR:  COPY FORCE_NULL requires CSV mode
+copy copytest to stdout (format json, on_error ignore);
+ERROR:  COPY ON_ERROR cannot be used with COPY TO
+LINE 1: copy copytest to stdout (format json, on_error ignore);
+                                              ^
+copy copytest from stdin(format json);
+ERROR:  COPY json mode cannot be used with COPY FROM
+-- all of the above should yield error
+-- embedded escaped characters
+create temp table copyjsontest (
+    id bigserial,
+    f1 text,
+    f2 timestamptz);
+insert into copyjsontest
+  select g.i,
+         CASE WHEN g.i % 2 = 0 THEN
+           'line with '' in it: ' || g.i::text
+         ELSE
+           'line with " in it: ' || g.i::text
+         END,
+         'Mon Feb 10 17:32:01 1997 PST'
+  from generate_series(1,5) as g(i);
+insert into copyjsontest (f1) values
+(E'aaa\"bbb'::text),
+(E'aaa\\bbb'::text),
+(E'aaa\/bbb'::text),
+(E'aaa\bbbb'::text),
+(E'aaa\fbbb'::text),
+(E'aaa\nbbb'::text),
+(E'aaa\rbbb'::text),
+(E'aaa\tbbb'::text);
+copy copyjsontest to stdout json;
+{"id":1,"f1":"line with \" in it: 1","f2":"1997-02-10T17:32:01-08:00"}
+{"id":2,"f1":"line with ' in it: 2","f2":"1997-02-10T17:32:01-08:00"}
+{"id":3,"f1":"line with \" in it: 3","f2":"1997-02-10T17:32:01-08:00"}
+{"id":4,"f1":"line with ' in it: 4","f2":"1997-02-10T17:32:01-08:00"}
+{"id":5,"f1":"line with \" in it: 5","f2":"1997-02-10T17:32:01-08:00"}
+{"id":1,"f1":"aaa\"bbb","f2":null}
+{"id":2,"f1":"aaa\\bbb","f2":null}
+{"id":3,"f1":"aaa/bbb","f2":null}
+{"id":4,"f1":"aaa\bbbb","f2":null}
+{"id":5,"f1":"aaa\fbbb","f2":null}
+{"id":6,"f1":"aaa\nbbb","f2":null}
+{"id":7,"f1":"aaa\rbbb","f2":null}
+{"id":8,"f1":"aaa\tbbb","f2":null}
 create temp table copytest4 (
 	c1 int,
 	"colname with tab: 	" text);
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index f1699b66b0..054fce95cb 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -82,6 +82,53 @@ this is just a line full of junk that would error out if parsed

+--- test copying in JSON mode with various styles
+copy copytest to stdout json;
+
+copy copytest to stdout (format json);
+
+-- all of the following should yield error
+copy copytest to stdout (format json, delimiter '|');
+copy copytest to stdout (format json, null '\N');
+copy copytest to stdout (format json, default '|');
+copy copytest to stdout (format json, header);
+copy copytest to stdout (format json, quote '"');
+copy copytest to stdout (format json, escape '"');
+copy copytest to stdout (format json, force_quote *);
+copy copytest to stdout (format json, force_not_null *);
+copy copytest to stdout (format json, force_null *);
+copy copytest to stdout (format json, on_error ignore);
+copy copytest from stdin(format json);
+-- all of the above should yield error
+
+-- embedded escaped characters
+create temp table copyjsontest (
+    id bigserial,
+    f1 text,
+    f2 timestamptz);
+
+insert into copyjsontest
+  select g.i,
+         CASE WHEN g.i % 2 = 0 THEN
+           'line with '' in it: ' || g.i::text
+         ELSE
+           'line with " in it: ' || g.i::text
+         END,
+         'Mon Feb 10 17:32:01 1997 PST'
+  from generate_series(1,5) as g(i);
+
+insert into copyjsontest (f1) values
+(E'aaa\"bbb'::text),
+(E'aaa\\bbb'::text),
+(E'aaa\/bbb'::text),
+(E'aaa\bbbb'::text),
+(E'aaa\fbbb'::text),
+(E'aaa\nbbb'::text),
+(E'aaa\rbbb'::text),
+(E'aaa\tbbb'::text);
+
+copy copyjsontest to stdout json;
+
 create temp table copytest4 (
 	c1 int,
 	"colname with tab: 	" text);
-- 
2.34.1

From 7f475554a544b1e031522e21477731286deb9917 Mon Sep 17 00:00:00 2001
From: Joel Jacobson <[email-masked]>
Date: Thu, 24 Oct 2024 08:24:13 +0300
Subject: [PATCH v14 1/3] Introduce CopyFormat and replace csv_mode and binary
 fields with it.

---
 src/backend/commands/copy.c          | 50 +++++++++++++++-------------
 src/backend/commands/copyfrom.c      | 10 +++---
 src/backend/commands/copyfromparse.c | 34 +++++++++----------
 src/backend/commands/copyto.c        | 20 +++++------
 src/include/commands/copy.h          | 13 ++++++--
 src/tools/pgindent/typedefs.list     |  1 +
 6 files changed, 70 insertions(+), 58 deletions(-)

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index cfca9d9dc2..e7e7815853 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -525,11 +525,11 @@ ProcessCopyOptions(ParseState *pstate,
 				errorConflictingDefElem(defel, pstate);
 			format_specified = true;
 			if (strcmp(fmt, "text") == 0)
-				 /* default format */ ;
+				opts_out->format = COPY_FORMAT_TEXT;
 			else if (strcmp(fmt, "csv") == 0)
-				opts_out->csv_mode = true;
+				opts_out->format = COPY_FORMAT_CSV;
 			else if (strcmp(fmt, "binary") == 0)
-				opts_out->binary = true;
+				opts_out->format = COPY_FORMAT_BINARY;
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -689,31 +689,31 @@ ProcessCopyOptions(ParseState *pstate,
 	 * Check for incompatible options (must do these three before inserting
 	 * defaults)
 	 */
-	if (opts_out->binary && opts_out->delim)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->delim)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("cannot specify %s in BINARY mode", "DELIMITER")));
 
-	if (opts_out->binary && opts_out->null_print)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->null_print)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("cannot specify %s in BINARY mode", "NULL")));
 
-	if (opts_out->binary && opts_out->default_print)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->default_print)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("cannot specify %s in BINARY mode", "DEFAULT")));
 
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
-		opts_out->delim = opts_out->csv_mode ? "," : "\t";
+		opts_out->delim = opts_out->format == COPY_FORMAT_CSV ? "," : "\t";
 
 	if (!opts_out->null_print)
-		opts_out->null_print = opts_out->csv_mode ? "" : "\\N";
+		opts_out->null_print = opts_out->format == COPY_FORMAT_CSV ? "" : "\\N";
 	opts_out->null_print_len = strlen(opts_out->null_print);
 
-	if (opts_out->csv_mode)
+	if (opts_out->format == COPY_FORMAT_CSV)
 	{
 		if (!opts_out->quote)
 			opts_out->quote = "\"";
@@ -761,7 +761,7 @@ ProcessCopyOptions(ParseState *pstate,
 	 * future-proofing.  Likewise we disallow all digits though only octal
 	 * digits are actually dangerous.
 	 */
-	if (!opts_out->csv_mode &&
+	if (opts_out->format != COPY_FORMAT_CSV &&
 		strchr("\\.abcdefghijklmnopqrstuvwxyz0123456789",
 			   opts_out->delim[0]) != NULL)
 		ereport(ERROR,
@@ -769,43 +769,44 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
-	if (opts_out->binary && opts_out->header_line)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->header_line)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("cannot specify %s in BINARY mode", "HEADER")));
 
 	/* Check quote */
-	if (!opts_out->csv_mode && opts_out->quote != NULL)
+	if (opts_out->format != COPY_FORMAT_CSV && opts_out->quote != NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("COPY %s requires CSV mode", "QUOTE")));
 
-	if (opts_out->csv_mode && strlen(opts_out->quote) != 1)
+	if (opts_out->format == COPY_FORMAT_CSV && strlen(opts_out->quote) != 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("COPY quote must be a single one-byte character")));
 
-	if (opts_out->csv_mode && opts_out->delim[0] == opts_out->quote[0])
+	if (opts_out->format == COPY_FORMAT_CSV && opts_out->delim[0] == opts_out->quote[0])
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("COPY delimiter and quote must be different")));
 
 	/* Check escape */
-	if (!opts_out->csv_mode && opts_out->escape != NULL)
+	if (opts_out->format != COPY_FORMAT_CSV && opts_out->escape != NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("COPY %s requires CSV mode", "ESCAPE")));
 
-	if (opts_out->csv_mode && strlen(opts_out->escape) != 1)
+	if (opts_out->format == COPY_FORMAT_CSV && strlen(opts_out->escape) != 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("COPY escape must be a single one-byte character")));
 
 	/* Check force_quote */
-	if (!opts_out->csv_mode && (opts_out->force_quote || opts_out->force_quote_all))
+	if (opts_out->format != COPY_FORMAT_CSV && (opts_out->force_quote ||
+												opts_out->force_quote_all))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
@@ -819,8 +820,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
 	/* Check force_notnull */
-	if (!opts_out->csv_mode && (opts_out->force_notnull != NIL ||
-								opts_out->force_notnull_all))
+	if (opts_out->format != COPY_FORMAT_CSV &&
+		(opts_out->force_notnull != NIL || opts_out->force_notnull_all))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
@@ -835,8 +836,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
-	if (!opts_out->csv_mode && (opts_out->force_null != NIL ||
-								opts_out->force_null_all))
+	if (opts_out->format != COPY_FORMAT_CSV && (opts_out->force_null != NIL ||
+												opts_out->force_null_all))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
@@ -860,7 +861,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
 	/* Don't allow the CSV quote char to appear in the null string. */
-	if (opts_out->csv_mode &&
+	if (opts_out->format == COPY_FORMAT_CSV &&
 		strchr(opts_out->null_print, opts_out->quote[0]) != NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -896,7 +897,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
 		/* Don't allow the CSV quote char to appear in the default string. */
-		if (opts_out->csv_mode &&
+		if (opts_out->format == COPY_FORMAT_CSV &&
 			strchr(opts_out->default_print, opts_out->quote[0]) != NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -913,7 +914,8 @@ ProcessCopyOptions(ParseState *pstate,
 					 errmsg("NULL specification and DEFAULT specification cannot be the same")));
 	}
 	/* Check on_error */
-	if (opts_out->binary && opts_out->on_error != COPY_ON_ERROR_STOP)
+	if (opts_out->format == COPY_FORMAT_BINARY &&
+		opts_out->on_error != COPY_ON_ERROR_STOP)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("only ON_ERROR STOP is allowed in BINARY mode")));
diff --git a/src/backend/commands/copyfrom.c b/src/backend/commands/copyfrom.c
index 0cbd05f560..aea807d13c 100644
--- a/src/backend/commands/copyfrom.c
+++ b/src/backend/commands/copyfrom.c
@@ -122,7 +122,7 @@ CopyFromErrorCallback(void *arg)
 				   cstate->cur_relname);
 		return;
 	}
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* can't usefully display the data */
 		if (cstate->cur_attname)
@@ -1583,7 +1583,7 @@ BeginCopyFrom(ParseState *pstate,
 	cstate->raw_buf_index = cstate->raw_buf_len = 0;
 	cstate->raw_reached_eof = false;
 
-	if (!cstate->opts.binary)
+	if (cstate->opts.format != COPY_FORMAT_BINARY)
 	{
 		/*
 		 * If encoding conversion is needed, we need another buffer to hold
@@ -1634,7 +1634,7 @@ BeginCopyFrom(ParseState *pstate,
 			continue;
 
 		/* Fetch the input function and typioparam info */
-		if (cstate->opts.binary)
+		if (cstate->opts.format == COPY_FORMAT_BINARY)
 			getTypeBinaryInputInfo(att->atttypid,
 								   &in_func_oid, &typioparams[attnum - 1]);
 		else
@@ -1775,14 +1775,14 @@ BeginCopyFrom(ParseState *pstate,
 
 	pgstat_progress_update_multi_param(3, progress_cols, progress_vals);
 
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* Read and verify binary header */
 		ReceiveCopyBinaryHeader(cstate);
 	}
 
 	/* create workspace for CopyReadAttributes results */
-	if (!cstate->opts.binary)
+	if (cstate->opts.format != COPY_FORMAT_BINARY)
 	{
 		AttrNumber	attr_count = list_length(cstate->attnumlist);
 
diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index caccdc8563..5b56aa89e3 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -162,7 +162,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 {
 	StringInfoData buf;
 	int			natts = list_length(cstate->attnumlist);
-	int16		format = (cstate->opts.binary ? 1 : 0);
+	int16		format = (cstate->opts.format == COPY_FORMAT_BINARY ? 1 : 0);
 	int			i;
 
 	pq_beginmessage(&buf, PqMsg_CopyInResponse);
@@ -748,7 +748,7 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 	bool		done;
 
 	/* only available for text or csv input */
-	Assert(!cstate->opts.binary);
+	Assert(cstate->opts.format != COPY_FORMAT_BINARY);
 
 	/* on input check that the header line is correct if needed */
 	if (cstate->cur_lineno == 0 && cstate->opts.header_line)
@@ -765,7 +765,7 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 		{
 			int			fldnum;
 
-			if (cstate->opts.csv_mode)
+			if (cstate->opts.format == COPY_FORMAT_CSV)
 				fldct = CopyReadAttributesCSV(cstate);
 			else
 				fldct = CopyReadAttributesText(cstate);
@@ -820,7 +820,7 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 		return false;
 
 	/* Parse the line into de-escaped field values */
-	if (cstate->opts.csv_mode)
+	if (cstate->opts.format == COPY_FORMAT_CSV)
 		fldct = CopyReadAttributesCSV(cstate);
 	else
 		fldct = CopyReadAttributesText(cstate);
@@ -864,7 +864,7 @@ NextCopyFrom(CopyFromState cstate, ExprContext *econtext,
 	MemSet(nulls, true, num_phys_attrs * sizeof(bool));
 	MemSet(cstate->defaults, false, num_phys_attrs * sizeof(bool));
 
-	if (!cstate->opts.binary)
+	if (cstate->opts.format != COPY_FORMAT_BINARY)
 	{
 		char	  **field_strings;
 		ListCell   *cur;
@@ -905,7 +905,7 @@ NextCopyFrom(CopyFromState cstate, ExprContext *econtext,
 				continue;
 			}
 
-			if (cstate->opts.csv_mode)
+			if (cstate->opts.format == COPY_FORMAT_CSV)
 			{
 				if (string == NULL &&
 					cstate->opts.force_notnull_flags[m])
@@ -1178,7 +1178,7 @@ CopyReadLineText(CopyFromState cstate)
 	char		quotec = '\0';
 	char		escapec = '\0';
 
-	if (cstate->opts.csv_mode)
+	if (cstate->opts.format == COPY_FORMAT_CSV)
 	{
 		quotec = cstate->opts.quote[0];
 		escapec = cstate->opts.escape[0];
@@ -1255,7 +1255,7 @@ CopyReadLineText(CopyFromState cstate)
 		prev_raw_ptr = input_buf_ptr;
 		c = copy_input_buf[input_buf_ptr++];
 
-		if (cstate->opts.csv_mode)
+		if (cstate->opts.format == COPY_FORMAT_CSV)
 		{
 			/*
 			 * If character is '\r', we may need to look ahead below.  Force
@@ -1294,7 +1294,7 @@ CopyReadLineText(CopyFromState cstate)
 		}
 
 		/* Process \r */
-		if (c == '\r' && (!cstate->opts.csv_mode || !in_quote))
+		if (c == '\r' && (cstate->opts.format != COPY_FORMAT_CSV || !in_quote))
 		{
 			/* Check for \r\n on first line, _and_ handle \r\n. */
 			if (cstate->eol_type == EOL_UNKNOWN ||
@@ -1322,10 +1322,10 @@ CopyReadLineText(CopyFromState cstate)
 					if (cstate->eol_type == EOL_CRNL)
 						ereport(ERROR,
 								(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
-								 !cstate->opts.csv_mode ?
+								 cstate->opts.format != COPY_FORMAT_CSV ?
 								 errmsg("literal carriage return found in data") :
 								 errmsg("unquoted carriage return found in data"),
-								 !cstate->opts.csv_mode ?
+								 cstate->opts.format != COPY_FORMAT_CSV ?
 								 errhint("Use \"\\r\" to represent carriage return.") :
 								 errhint("Use quoted CSV field to represent carriage return.")));
 
@@ -1339,10 +1339,10 @@ CopyReadLineText(CopyFromState cstate)
 			else if (cstate->eol_type == EOL_NL)
 				ereport(ERROR,
 						(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
-						 !cstate->opts.csv_mode ?
+						 cstate->opts.format != COPY_FORMAT_CSV ?
 						 errmsg("literal carriage return found in data") :
 						 errmsg("unquoted carriage return found in data"),
-						 !cstate->opts.csv_mode ?
+						 cstate->opts.format != COPY_FORMAT_CSV ?
 						 errhint("Use \"\\r\" to represent carriage return.") :
 						 errhint("Use quoted CSV field to represent carriage return.")));
 			/* If reach here, we have found the line terminator */
@@ -1350,15 +1350,15 @@ CopyReadLineText(CopyFromState cstate)
 		}
 
 		/* Process \n */
-		if (c == '\n' && (!cstate->opts.csv_mode || !in_quote))
+		if (c == '\n' && (cstate->opts.format != COPY_FORMAT_CSV || !in_quote))
 		{
 			if (cstate->eol_type == EOL_CR || cstate->eol_type == EOL_CRNL)
 				ereport(ERROR,
 						(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
-						 !cstate->opts.csv_mode ?
+						 cstate->opts.format != COPY_FORMAT_CSV ?
 						 errmsg("literal newline found in data") :
 						 errmsg("unquoted newline found in data"),
-						 !cstate->opts.csv_mode ?
+						 cstate->opts.format != COPY_FORMAT_CSV ?
 						 errhint("Use \"\\n\" to represent newline.") :
 						 errhint("Use quoted CSV field to represent newline.")));
 			cstate->eol_type = EOL_NL;	/* in case not set yet */
@@ -1370,7 +1370,7 @@ CopyReadLineText(CopyFromState cstate)
 		 * Process backslash, except in CSV mode where backslash is a normal
 		 * character.
 		 */
-		if (c == '\\' && !cstate->opts.csv_mode)
+		if (c == '\\' && cstate->opts.format != COPY_FORMAT_CSV)
 		{
 			char		c2;
 
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 99cb23cb34..ea90af28a9 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -134,7 +134,7 @@ SendCopyBegin(CopyToState cstate)
 {
 	StringInfoData buf;
 	int			natts = list_length(cstate->attnumlist);
-	int16		format = (cstate->opts.binary ? 1 : 0);
+	int16		format = (cstate->opts.format == COPY_FORMAT_BINARY ? 1 : 0);
 	int			i;
 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
@@ -191,7 +191,7 @@ CopySendEndOfRow(CopyToState cstate)
 	switch (cstate->copy_dest)
 	{
 		case COPY_FILE:
-			if (!cstate->opts.binary)
+			if (cstate->opts.format != COPY_FORMAT_BINARY)
 			{
 				/* Default line termination depends on platform */
 #ifndef WIN32
@@ -236,7 +236,7 @@ CopySendEndOfRow(CopyToState cstate)
 			break;
 		case COPY_FRONTEND:
 			/* The FE/BE protocol uses \n as newline for all platforms */
-			if (!cstate->opts.binary)
+			if (cstate->opts.format != COPY_FORMAT_BINARY)
 				CopySendChar(cstate, '\n');
 
 			/* Dump the accumulated row as one CopyData message */
@@ -775,7 +775,7 @@ DoCopyTo(CopyToState cstate)
 		bool		isvarlena;
 		Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);
 
-		if (cstate->opts.binary)
+		if (cstate->opts.format == COPY_FORMAT_BINARY)
 			getTypeBinaryOutputInfo(attr->atttypid,
 									&out_func_oid,
 									&isvarlena);
@@ -796,7 +796,7 @@ DoCopyTo(CopyToState cstate)
 											   "COPY TO",
 											   ALLOCSET_DEFAULT_SIZES);
 
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* Generate header for a binary copy */
 		int32		tmp;
@@ -837,7 +837,7 @@ DoCopyTo(CopyToState cstate)
 
 				colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);
 
-				if (cstate->opts.csv_mode)
+				if (cstate->opts.format == COPY_FORMAT_CSV)
 					CopyAttributeOutCSV(cstate, colname, false);
 				else
 					CopyAttributeOutText(cstate, colname);
@@ -884,7 +884,7 @@ DoCopyTo(CopyToState cstate)
 		processed = ((DR_copy *) cstate->queryDesc->dest)->processed;
 	}
 
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* Generate trailer for a binary copy */
 		CopySendInt16(cstate, -1);
@@ -912,7 +912,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	MemoryContextReset(cstate->rowcontext);
 	oldcontext = MemoryContextSwitchTo(cstate->rowcontext);
 
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* Binary per-tuple header */
 		CopySendInt16(cstate, list_length(cstate->attnumlist));
@@ -921,7 +921,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 	/* Make sure the tuple is fully deconstructed */
 	slot_getallattrs(slot);
 
-	if (!cstate->opts.binary)
+	if (cstate->opts.format != COPY_FORMAT_BINARY)
 	{
 		bool		need_delim = false;
 
@@ -941,7 +941,7 @@ CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
 			{
 				string = OutputFunctionCall(&out_functions[attnum - 1],
 											value);
-				if (cstate->opts.csv_mode)
+				if (cstate->opts.format == COPY_FORMAT_CSV)
 					CopyAttributeOutCSV(cstate, string,
 										cstate->opts.force_quote_flags[attnum - 1]);
 				else
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 06dfdfef72..7a1ee65601 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -51,6 +51,16 @@ typedef enum CopyLogVerbosityChoice
 	COPY_LOG_VERBOSITY_VERBOSE, /* logs additional messages */
 } CopyLogVerbosityChoice;
 
+/*
+ * Represents the format of the COPY operation.
+ */
+typedef enum CopyFormat
+{
+	COPY_FORMAT_TEXT = 0,
+	COPY_FORMAT_BINARY,
+	COPY_FORMAT_CSV,
+} CopyFormat;
+
 /*
  * A struct to hold COPY options, in a parsed form. All of these are related
  * to formatting, except for 'freeze', which doesn't really belong here, but
@@ -61,9 +71,8 @@ typedef struct CopyFormatOptions
 	/* parameters from the COPY command */
 	int			file_encoding;	/* file or remote side's character encoding,
 								 * -1 if not specified */
-	bool		binary;			/* binary format? */
+	CopyFormat	format;			/* format of the COPY operation */
 	bool		freeze;			/* freeze rows on loading? */
-	bool		csv_mode;		/* Comma Separated Value format? */
 	CopyHeaderChoice header_line;	/* header line? */
 	char	   *null_print;		/* NULL marker string (server encoding!) */
 	int			null_print_len; /* length of same */
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index a2644a2e65..d88382cdcc 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -496,6 +496,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromState
 CopyFromStateData
-- 
2.34.1

---

From: Junwang Zhao <[email-masked]>
Date: Sun, 2 Mar 2025 13:28:07 +0800

> the following are the benchmarks info:

I've refactored the patch to adapt the newly introduced CopyToRoutine struct,
see 2e4127b6d2.

v15-0001 is the merged one of v14-0001 and v14-0002

There are some other ongoing *copy to/from* refactors[1] which we can benefit
to make the code cleaner, especially the checks done in ProcessCopyOptions.

[1]: https://www.postgresql.org/message-id/20250301.115009.424844407736647598.kou%40clear-code.com

-- 
Regards
Junwang Zhao

---

From: jian he <[email-masked]>
Date: Tue, 11 Mar 2025 16:23:42 +0800

hi.

git apply --check $PATCHES/v15-0001-Introduce-json-format-for-COPY-TO.patch
error: patch failed: src/backend/commands/copyfrom.c:155
error: src/backend/commands/copyfrom.c: patch does not apply
error: patch failed: src/backend/commands/copyto.c:176
error: src/backend/commands/copyto.c: patch does not apply

seems to need rebase.
the attachment is the rebase, minor comments tweaks, and commit message tweaks.

another issue is this patch entry in commitfest [1] status is: Not processed,
which means no cfbots CI tests, seems not great.
not sure how to resolve this issue....

[1] https://commitfest.postgresql.org/patch/4716/
From 24e1858722dbb25c4842d0ec2dee5b1047edcc23 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Tue, 11 Mar 2025 16:19:55 +0800
Subject: [PATCH v16 2/2] Add option force_array for COPY JSON FORMAT

refactored by Junwang Zhao to adapt the newly introduced CopyToRoutine struct(2e4127b6d2).

Author: Joe Conway <[email-masked]>
discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 14 ++++++++++++
 src/backend/commands/copy.c        | 13 ++++++++++++
 src/backend/commands/copyto.c      | 34 +++++++++++++++++++++++++++++-
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 23 ++++++++++++++++++++
 src/test/regress/sql/copy.sql      |  8 +++++++
 7 files changed, 93 insertions(+), 2 deletions(-)

index 9c519d8a9e2..7b3c913d4ee 100644
 
+   <varlistentry>
index b6f74c798d0..7b4c64ea97e 100644
 
@@ -906,6 +914,11 @@ ProcessCopyOptions(ParseState *pstate,
 
index c1d4cbeedea..393c0440ad7 100644
@@ -84,6 +84,7 @@ typedef struct CopyToStateData
 
 	CopyFormatOptions opts;
@@ -128,6 +129,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
 static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
+static void CopyToJsonEnd(CopyToState cstate);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -172,7 +174,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 	.CopyToStart = CopyToTextLikeStart,
 	.CopyToOutFunc = CopyToTextLikeOutFunc,
 	.CopyToOneRow = CopyToJsonOneRow,
-	.CopyToEnd = CopyToTextLikeEnd,
+	.CopyToEnd = CopyToJsonEnd,
 };
 
 /* binary format */
@@ -238,6 +240,16 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 
 		CopySendTextLikeEndOfRow(cstate);
 	}
+
+	/*
+	 * If JSON has been requested, and FORCE_ARRAY has been specified send
+	 * the opening bracket.
+	 */
+	if (cstate->opts.format == COPY_FORMAT_JSON && cstate->opts.force_array)
+	{
+		CopySendChar(cstate, '[');
+		CopySendTextLikeEndOfRow(cstate);
+	}
 }
 
 /*
@@ -349,11 +361,31 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	result = makeStringInfo();
 	composite_to_json(rowdata, result, false);

 	CopySendTextLikeEndOfRow(cstate);
 }
 
+/* Implementation of the end callback for json format */
+static void
+CopyToJsonEnd(CopyToState cstate)
+{
+	if (cstate->opts.force_array)
+	{
+		CopySendChar(cstate, ']');
+		CopySendTextLikeEndOfRow(cstate);
+	}
+}
+
 /*
  * Implementation of the start callback for binary format. Send a header
  * for a binary copy.
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 6069b118834..e0c7412ec0a 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3278,7 +3278,7 @@ match_previous_words(int pattern_id,
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "("))
 		COMPLETE_WITH("FORMAT", "FREEZE", "DELIMITER", "NULL",
 					  "HEADER", "QUOTE", "ESCAPE", "FORCE_QUOTE",
-					  "FORCE_NOT_NULL", "FORCE_NULL", "ENCODING", "DEFAULT",
+					  "FORCE_NOT_NULL", "FORCE_NULL", "FORCE_ARRAY", "ENCODING", "DEFAULT",
 					  "ON_ERROR", "LOG_VERBOSITY");
 
index 07fcc2bc9ac..fa8a8ab7e31 100644
@@ -89,6 +89,7 @@ typedef struct CopyFormatOptions
 	List	   *force_notnull;	/* list of column names */
 	bool		force_notnull_all;	/* FORCE_NOT_NULL *? */
 	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
index 0d4cfc0b60a..3d0781700b3 100644
index 6ee96f5aa51..2781c24bd84 100644
@@ -101,6 +101,14 @@ copy copytest to stdout (format json, on_error ignore);
 
+--Error

From 71cf17c9d1aefecc89cc388b979bbfc9952898c8 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Tue, 11 Mar 2025 15:53:37 +0800
Subject: [PATCH v16 1/2] Introduce json format for COPY TO

CopyFormat enum part was coied from Joel Jacobson <[email-masked]>
refactored by Jian He to fix some miscellaneous issue.
refactored by Junwang Zhao to adapt the newly introduced CopyToRoutine struct(2e4127b6d2).

Author: Joe Conway <[email-masked]>
Reviewed-by: "Andrey M. Borodin" <[email-masked]>,
Reviewed-by: Dean Rasheed <[email-masked]>,
Reviewed-by: Daniel Verite <[email-masked]>,
Reviewed-by: Andrew Dunstan <[email-masked]>,
Reviewed-by: Davin Shearer <[email-masked]>,
Reviewed-by: Masahiko Sawada <[email-masked]>,
Reviewed-by: Alvaro Herrera <[email-masked]>

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml           | 13 +++--
 src/backend/commands/copy.c          | 77 ++++++++++++++++++--------
 src/backend/commands/copyfrom.c      |  6 +-
 src/backend/commands/copyfromparse.c |  6 +-
 src/backend/commands/copyto.c        | 83 ++++++++++++++++++++++++----
 src/backend/parser/gram.y            |  8 +++
 src/backend/utils/adt/json.c         |  5 +-
 src/bin/psql/tab-complete.in.c       |  2 +-
 src/include/commands/copy.h          | 14 ++++-
 src/include/utils/json.h             |  2 +
 src/test/regress/expected/copy.out   | 74 +++++++++++++++++++++++++
 src/test/regress/sql/copy.sql        | 47 ++++++++++++++++
 src/tools/pgindent/typedefs.list     |  1 +
 13 files changed, 286 insertions(+), 52 deletions(-)

index df093da97c5..9c519d8a9e2 100644

      <note>
index cfca9d9dc29..b6f74c798d0 100644
@@ -525,11 +525,13 @@ ProcessCopyOptions(ParseState *pstate,
@@ -689,31 +691,47 @@ ProcessCopyOptions(ParseState *pstate,

 

@@ -761,7 +779,7 @@ ProcessCopyOptions(ParseState *pstate,
@@ -769,43 +787,48 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* Check header */

 
 
 	/* Check escape */

 	/* Check force_quote */
-	if (!opts_out->csv_mode && (opts_out->force_quote || opts_out->force_quote_all))
+	if (opts_out->format != COPY_FORMAT_CSV && (opts_out->force_quote || opts_out->force_quote_all))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
@@ -819,8 +842,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
 	/* Check force_notnull */
-	if (!opts_out->csv_mode && (opts_out->force_notnull != NIL ||
-								opts_out->force_notnull_all))
+	if (opts_out->format != COPY_FORMAT_CSV && (opts_out->force_notnull != NIL ||
+												opts_out->force_notnull_all))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
@@ -835,8 +858,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
@@ -860,7 +883,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
@@ -877,6 +900,12 @@ ProcessCopyOptions(ParseState *pstate,
 
@@ -896,7 +925,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
 		/* Don't allow the CSV quote char to appear in the default string. */
-		if (opts_out->csv_mode &&
+		if (opts_out->format == COPY_FORMAT_CSV &&
 			strchr(opts_out->default_print, opts_out->quote[0]) != NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -913,7 +942,7 @@ ProcessCopyOptions(ParseState *pstate,
 					 errmsg("NULL specification and DEFAULT specification cannot be the same")));
 	}
 	/* Check on_error */
-	if (opts_out->binary && opts_out->on_error != COPY_ON_ERROR_STOP)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->on_error != COPY_ON_ERROR_STOP)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("only ON_ERROR STOP is allowed in BINARY mode")));
diff --git a/src/backend/commands/copyfrom.c b/src/backend/commands/copyfrom.c
index bcf66f0adf8..bfe1937539b 100644
--- a/src/backend/commands/copyfrom.c
+++ b/src/backend/commands/copyfrom.c
@@ -155,9 +155,9 @@ static const CopyFromRoutine CopyFromRoutineBinary = {
 static const CopyFromRoutine *
 CopyFromGetRoutine(const CopyFormatOptions *opts)
 {
-	if (opts->csv_mode)
+	if (opts->format == COPY_FORMAT_CSV)
 		return &CopyFromRoutineCSV;
-	else if (opts->binary)
+	else if (opts->format == COPY_FORMAT_BINARY)
 		return &CopyFromRoutineBinary;
 
 	/* default is text */
@@ -261,7 +261,7 @@ CopyFromErrorCallback(void *arg)
 				   cstate->cur_relname);
 		return;
 	}
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* can't usefully display the data */
 		if (cstate->cur_attname)
diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index e8128f85e6b..02263f1b1f5 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -171,7 +171,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 {
 	StringInfoData buf;
 	int			natts = list_length(cstate->attnumlist);
-	int16		format = (cstate->opts.binary ? 1 : 0);
+	int16		format = (cstate->opts.format == COPY_FORMAT_BINARY ? 1 : 0);
 	int			i;
 
 	pq_beginmessage(&buf, PqMsg_CopyInResponse);
@@ -747,7 +747,7 @@ bool
 NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 {
 	return NextCopyFromRawFieldsInternal(cstate, fields, nfields,
-										 cstate->opts.csv_mode);
+										 cstate->opts.format == COPY_FORMAT_CSV);
 }
 
 /*
@@ -774,7 +774,7 @@ NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields
 	bool		done;
 
 	/* only available for text or csv input */
-	Assert(!cstate->opts.binary);
+	Assert(!(cstate->opts.format == COPY_FORMAT_BINARY));
 
 	/* on input check that the header line is correct if needed */
 	if (cstate->cur_lineno == 0 && cstate->opts.header_line)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 84a3f3879a8..c1d4cbeedea 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -24,6 +24,7 @@
 #include "executor/execdesc.h"
 #include "executor/executor.h"
 #include "executor/tuptable.h"
+#include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -31,6 +32,7 @@
 #include "pgstat.h"
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
+#include "utils/json.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -125,6 +127,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -144,7 +147,7 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 /*
  * COPY TO routines for built-in formats.
  *
- * CSV and text formats share the same TextLike routines except for the
+ * CSV and text, json formats share the same TextLike routines except for the
  * one-row callback.
  */
 
@@ -164,6 +167,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
+static const CopyToRoutine CopyToRoutineJson = {
+	.CopyToStart = CopyToTextLikeStart,
+	.CopyToOutFunc = CopyToTextLikeOutFunc,
+	.CopyToOneRow = CopyToJsonOneRow,
+	.CopyToEnd = CopyToTextLikeEnd,
+};
+
 /* binary format */
 static const CopyToRoutine CopyToRoutineBinary = {
 	.CopyToStart = CopyToBinaryStart,
@@ -176,16 +187,18 @@ static const CopyToRoutine CopyToRoutineBinary = {
 static const CopyToRoutine *
 CopyToGetRoutine(const CopyFormatOptions *opts)
 {
-	if (opts->csv_mode)
+	if (opts->format == COPY_FORMAT_CSV)
 		return &CopyToRoutineCSV;
-	else if (opts->binary)
+	else if (opts->format == COPY_FORMAT_BINARY)
 		return &CopyToRoutineBinary;
+	else if (opts->format == COPY_FORMAT_JSON)
+		return &CopyToRoutineJson;
 
 	/* default is text */
 	return &CopyToRoutineText;
 }
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -204,6 +217,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -215,7 +230,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

@@ -226,7 +241,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 }
 
 /*
- * Implementation of the outfunc callback for text and CSV formats. Assign
+ * Implementation of the outfunc callback for text, CSV, and json formats. Assign
  * the output function data to the given *finfo.
  */
 static void
@@ -299,13 +314,46 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }
 
-/* Implementation of the end callback for text and CSV formats */
+/* Implementation of the end callback for text, CSV, and json formats */
 static void
 CopyToTextLikeEnd(CopyToState cstate)
 {
 	/* Nothing to do here */
 }
 
+/* Implementation of per-row callback for json format */
+static void
+CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
+{
+	Datum		rowdata;
+	StringInfo	result;
+
+	/*
+	 * if the COPY TO source data come from query rather than plain table, we need
+	 * copy CopyToState->QueryDesc->TupleDesc to slot->tts_tupleDescriptor.
+	 * This is necessary because the slot's TupleDesc may change during query execution,
+	 * and we depend on it when calling composite_to_json.
+	 */
+	if (!cstate->rel)
+	{
+		memcpy(TupleDescAttr(slot->tts_tupleDescriptor, 0),
+			   TupleDescAttr(cstate->queryDesc->tupDesc, 0),
+			   cstate->queryDesc->tupDesc->natts * sizeof(FormData_pg_attribute));
+
+		for (int i = 0; i < cstate->queryDesc->tupDesc->natts; i++)
+			populate_compact_attribute(slot->tts_tupleDescriptor, i);
+
+		BlessTupleDesc(slot->tts_tupleDescriptor);
+	}
+	rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	result = makeStringInfo();
+	composite_to_json(rowdata, result, false);
+
+	CopySendData(cstate, result->data, result->len);
+
+	CopySendTextLikeEndOfRow(cstate);
+}
+
 /*
  * Implementation of the start callback for binary format. Send a header
  * for a binary copy.
@@ -392,14 +440,25 @@ SendCopyBegin(CopyToState cstate)
 {
 	StringInfoData buf;
 	int			natts = list_length(cstate->attnumlist);
-	int16		format = (cstate->opts.binary ? 1 : 0);
+	int16		format = (cstate->opts.format == COPY_FORMAT_BINARY ? 1 : 0);
 	int			i;
 
@@ -499,7 +558,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
- * Wrapper function of CopySendEndOfRow for text and CSV formats. Sends the
+ * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the
  * line termination and do common appropriate things for the end of row.
  */
 static inline void
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 271ae26cbaf..e26881bb13f 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3493,6 +3493,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("format", (Node *) makeString("csv"), @1);
 				}
+			| JSON
+				{
+					$$ = makeDefElem("format", (Node *) makeString("json"), @1);
+				}
 			| HEADER_P
 				{
 					$$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3575,6 +3579,10 @@ copy_generic_opt_elem:
 				{
 					$$ = makeDefElem($1, $2, @1);
 				}
+			| FORMAT_LA copy_generic_opt_arg
+				{
+					$$ = makeDefElem("format", $2, @1);
+				}
 		;
 
 copy_generic_opt_arg:
index 51452755f58..bf69347fa94 100644

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 8432be641ac..6069b118834 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3283,7 +3283,7 @@ match_previous_words(int pattern_id,

 	/* Complete COPY <sth> FROM filename WITH (ON_ERROR */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "(", "ON_ERROR"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 06dfdfef721..07fcc2bc9ac 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -51,6 +51,17 @@ typedef enum CopyLogVerbosityChoice
 	COPY_LOG_VERBOSITY_VERBOSE, /* logs additional messages */
 } CopyLogVerbosityChoice;
 
+/*
@@ -61,9 +72,8 @@ typedef struct CopyFormatOptions
index 49bbda7ac06..1fa8e2ce8e2 100644
 
index 06bae8c61ae..0d4cfc0b60a 100644
index 3009bdfdf89..6ee96f5aa51 100644

index 9840060997f..a2e4bfee0e2 100644
@@ -500,6 +500,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.34.1

---

From: jian he <[email-masked]>
Date: Fri, 4 Jul 2025 13:27:08 +0800

On Tue, Mar 11, 2025 at 4:23 PM jian he <[email-masked]> wrote:

hi.
rebase and minor tweaks.
From 44c494fd8d7fdb9d8fd5d2d2a48f49b779d1bcb9 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Fri, 4 Jul 2025 13:25:00 +0800
Subject: [PATCH v17 2/2] Add option force_array for COPY JSON FORMAT

force_array option can only be used in COPY TO with JSON format.  it make the
output json output behave like json array type.  refactored by Junwang Zhao to
adapt the newly introduced CopyToRoutine struct(2e4127b6d2).

Author: Joe Conway <[email-masked]>
discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 14 +++++++++++
 src/backend/commands/copy.c        | 13 +++++++++++
 src/backend/commands/copyto.c      | 37 +++++++++++++++++++++++++++++-
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 23 +++++++++++++++++++
 src/test/regress/sql/copy.sql      |  8 +++++++
 7 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 219604ad306..c01927864bd 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -40,6 +40,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     HEADER [ <replaceable class="parameter">boolean</replaceable> | <replaceable class="parameter">integer</replaceable> | MATCH ]
     QUOTE '<replaceable class="parameter">quote_character</replaceable>'
     ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
+    FORCE_ARRAY [ <replaceable class="parameter">boolean</replaceable> ]
     FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NOT_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NULL { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
@@ -366,6 +367,19 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>FORCE_ARRAY</literal></term>
+    <listitem>
+     <para>
+      Force output of square brackets as array decorations at the beginning
+      and end of output, and commas between the rows. It is allowed only in
+      <command>COPY TO</command>, and only when using
+      <literal>json</literal> format. The default is
+      <literal>false</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>FORCE_QUOTE</literal></term>
     <listitem>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 213e59cc435..d23ef99e395 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -514,6 +514,7 @@ ProcessCopyOptions(ParseState *pstate,
 	bool		on_error_specified = false;
 	bool		log_verbosity_specified = false;
 	bool		reject_limit_specified = false;
+	bool		force_array_specified = false;
 	ListCell   *option;
 
 	/* Support external use for option sanity checking */
@@ -670,6 +671,13 @@ ProcessCopyOptions(ParseState *pstate,
 								defel->defname),
 						 parser_errposition(pstate, defel->location)));
 		}
+		else if (strcmp(defel->defname, "force_array") == 0)
+		{
+			if (force_array_specified)
+				errorConflictingDefElem(defel, pstate);
+			force_array_specified = true;
+			opts_out->force_array = defGetBoolean(defel);
+		}
 		else if (strcmp(defel->defname, "on_error") == 0)
 		{
 			if (on_error_specified)
@@ -918,6 +926,11 @@ ProcessCopyOptions(ParseState *pstate,
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				errmsg("COPY %s mode cannot be used with %s", "json", "COPY FROM"));
 
+	if (opts_out->format != COPY_FORMAT_JSON && opts_out->force_array)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s can only used with JSON mode", "FORCE_ARRAY"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 34b72936bca..18061661fb1 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -84,6 +84,10 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+
+	/* need delimiter to start next json array element */
+	bool		json_row_delim_needed;
+
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -128,6 +132,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
@@ -172,7 +177,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 
 /* binary format */
@@ -238,6 +243,16 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 
+	 * opening bracket.
 
 /*
@@ -349,11 +364,31 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	result = makeStringInfo();
 	composite_to_json(rowdata, result, false);

 
index bd4c03be050..55313612398 100644
@@ -3303,7 +3303,7 @@ match_previous_words(int pattern_id,
 					  "ON_ERROR", "LOG_VERBOSITY", "REJECT_LIMIT");
 
index 85aedc267d6..7274b0d3ca5 100644
@@ -87,6 +87,7 @@ typedef struct CopyFormatOptions
index fcb8823e101..f3196fd5609 100644
index 80bd4a59239..c55aa08e99d 100644
@@ -100,6 +100,14 @@ copy copytest to stdout (format json, on_error ignore);
 
+--Error

From 984846c42dee4da6bd718cc24031bc0272d62f12 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Fri, 4 Jul 2025 13:23:30 +0800
Subject: [PATCH v17 1/2] json format for COPY TO

JSON format is only supported with the COPY TO operation. It is incompatible
with options such as HEADER, DEFAULT, NULL, DELIMITER, and several others. This
has been thoroughly tested in src/test/regress/sql/copy.sql

The CopyFormat enum was originally contributed by Joel Jacobson
[email-masked], later refactored by Jian He to address various issues, and
further adapted by Junwang Zhao to support the newly introduced CopyToRoutine
struct (commit 2e4127b6d2).

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml           | 13 +++--
 src/backend/commands/copy.c          | 79 ++++++++++++++++++--------
 src/backend/commands/copyfrom.c      |  6 +-
 src/backend/commands/copyfromparse.c |  7 ++-
 src/backend/commands/copyto.c        | 83 ++++++++++++++++++++++++----
 src/backend/parser/gram.y            |  8 +++
 src/backend/utils/adt/json.c         |  5 +-
 src/bin/psql/tab-complete.in.c       |  2 +-
 src/include/commands/copy.h          | 14 ++++-
 src/include/utils/json.h             |  2 +
 src/test/regress/expected/copy.out   | 74 +++++++++++++++++++++++++
 src/test/regress/sql/copy.sql        | 46 +++++++++++++++
 src/tools/pgindent/typedefs.list     |  1 +
 13 files changed, 288 insertions(+), 52 deletions(-)

index c2d1fbc1fbe..219604ad306 100644
@@ -228,10 +228,15 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
 
@@ -266,7 +271,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
@@ -280,7 +285,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
 
      <note>
@@ -303,7 +308,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       is found in the input file, the default value of the corresponding column
       will be used.
       This option is allowed only in <command>COPY FROM</command>, and only when
-      not using <literal>binary</literal> format.
+      not using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
@@ -330,7 +335,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       <command>COPY FROM</command> commands.
      </para>
      <para>
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index fae9c41db65..213e59cc435 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -521,6 +521,8 @@ ProcessCopyOptions(ParseState *pstate,
 		opts_out = (CopyFormatOptions *) palloc0(sizeof(CopyFormatOptions));
 
 	opts_out->file_encoding = -1;
+	/* default format */
+	opts_out->format = COPY_FORMAT_TEXT;
 
 	/* Extract options from the statement node tree */
 	foreach(option, options)
@@ -535,11 +537,13 @@ ProcessCopyOptions(ParseState *pstate,
@@ -699,31 +703,47 @@ ProcessCopyOptions(ParseState *pstate,

 

@@ -771,7 +791,7 @@ ProcessCopyOptions(ParseState *pstate,
@@ -779,43 +799,48 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* Check header */
-	if (opts_out->binary && opts_out->header_line != COPY_HEADER_FALSE)
+	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->header_line != COPY_HEADER_FALSE)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
 				 errmsg("cannot specify %s in BINARY mode", "HEADER")));

 
 
 	/* Check escape */

 	/* Check force_quote */
@@ -829,8 +854,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
@@ -845,8 +870,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
@@ -870,7 +895,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
@@ -887,6 +912,12 @@ ProcessCopyOptions(ParseState *pstate,
 
+	/* Check json format  */
+	if (opts_out->format == COPY_FORMAT_JSON && is_from)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s mode cannot be used with %s", "json", "COPY FROM"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
@@ -906,7 +937,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
@@ -923,7 +954,7 @@ ProcessCopyOptions(ParseState *pstate,
index fbbbc09a97b..6c4bd303841 100644
 
 	/* default is text */
index b1ae97b833d..578e6c0c9a2 100644

 /*
@@ -774,7 +774,8 @@ NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields
 	bool		done = false;
 
 	/* only available for text or csv input */
-	Assert(!cstate->opts.binary);
+	Assert(cstate->opts.format == COPY_FORMAT_TEXT ||
+		   cstate->opts.format == COPY_FORMAT_CSV);
 
 	if (cstate->cur_lineno == 0 && cstate->opts.header_line != COPY_HEADER_FALSE)
index 67b94b91cae..34b72936bca 100644

+/* json format */
 
 	/* default is text */

 

 /*

+	 * if the COPY TO source data come from query rather than plain table, we
+	 * need copy CopyToState->QueryDesc->TupleDesc to slot->tts_tupleDescriptor.
+	 * This is necessary because the slot's TupleDesc may change during query
+	 * execution, and we depend on it when calling composite_to_json.

 /*
index 70a0d832a11..de0f5eb4118 100644
@@ -3492,6 +3492,10 @@ copy_opt_item:
@@ -3574,6 +3578,10 @@ copy_generic_opt_elem:
 
 copy_generic_opt_arg:

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 53e7d35fe98..bd4c03be050 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3308,7 +3308,7 @@ match_previous_words(int pattern_id,

 	/* Complete COPY <sth> FROM filename WITH (ON_ERROR */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "(", "ON_ERROR"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 541176e1980..85aedc267d6 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -48,6 +48,17 @@ typedef enum CopyLogVerbosityChoice
 	COPY_LOG_VERBOSITY_VERBOSE, /* logs additional messages */
 } CopyLogVerbosityChoice;
 
+/*
@@ -58,9 +69,8 @@ typedef struct CopyFormatOptions
 	int			header_line;	/* number of lines to skip or COPY_HEADER_XXX
 								 * value (see the above) */
 
index ac66eb55aee..fcb8823e101 100644
index a1316c73bac..80bd4a59239 100644
@@ -82,6 +82,52 @@ this is just a line full of junk that would error out if parsed

index 114bdafafdf..fa7d7b9244a 100644
@@ -518,6 +518,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.34.1

---

From: jian he <[email-masked]>
Date: Sun, 10 Aug 2025 23:20:12 +0800

hi.

rebase and splitted into 3 patches.

v18-0001
+typedef enum CopyFormat
+{
+ COPY_FORMAT_TEXT = 0,
+ COPY_FORMAT_BINARY,
+ COPY_FORMAT_CSV,
+} CopyFormat;
remove CopyFormatOptions two boolean field
(binary, csv_mode)

v18-0002, v18-0003 is refactoring based on prior patch.
From e9104bcc0a6c4ca96df5ff3fdd3ae659885dd664 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 30 Jul 2025 19:50:41 +0800
Subject: [PATCH v18 3/3] Add option force_array for COPY JSON FORMAT

 
+   <varlistentry>
index 7fd41dba250..0a22272f3fe 100644
 
@@ -925,6 +933,11 @@ ProcessCopyOptions(ParseState *pstate,
 
index 13eb14debbd..6fc1d3e9fee 100644
 
 	CopyFormatOptions opts;
 
 /* binary format */

 /*

 
index 16db5373c5f..9c65376fc7e 100644
@@ -1212,7 +1212,7 @@ Copy_common_options, "DEFAULT", "FORCE_NOT_NULL", "FORCE_NULL", "FREEZE", \
 
 /* COPY TO options */
 #define Copy_to_options \
-Copy_common_options, "FORCE_QUOTE"
+Copy_common_options, "FORCE_QUOTE", "FORCE_ARRAY"
 
 /*
  * These object types were introduced later than our support cutoff of
index 0fc6e84352c..22626a13ba5 100644
@@ -112,6 +112,29 @@ LINE 1: copy copytest to stdout (format json, on_error ignore);
index 071986d427a..0f121b48f71 100644
 
+--Error

From e6bafe5eab9463b253e9697e0fbd82246c316a12 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sun, 10 Aug 2025 23:13:38 +0800
Subject: [PATCH v18 2/3] json format for COPY TO

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 13 +++--
 src/backend/commands/copy.c        | 72 +++++++++++++++++++++-------
 src/backend/commands/copyto.c      | 76 ++++++++++++++++++++++++++----
 src/backend/parser/gram.y          |  8 ++++
 src/backend/utils/adt/json.c       |  5 +-
 src/bin/psql/tab-complete.in.c     |  4 +-
 src/include/commands/copy.h        |  1 +
 src/include/utils/json.h           |  2 +
 src/test/regress/expected/copy.out | 76 ++++++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 47 ++++++++++++++++++
 src/tools/pgindent/typedefs.list   |  1 +
 11 files changed, 271 insertions(+), 34 deletions(-)

 
      <note>
@@ -303,7 +308,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       is found in the input file, the default value of the corresponding column
       will be used.
       This option is allowed only in <command>COPY FROM</command>, and only when
-      not using <literal>binary</literal> format.
+      not using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
@@ -330,7 +335,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       <command>COPY FROM</command> commands.
      </para>
      <para>
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 68f69cfb9df..7fd41dba250 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -542,6 +542,8 @@ ProcessCopyOptions(ParseState *pstate,
 				opts_out->format = COPY_FORMAT_CSV;
 			else if (strcmp(fmt, "binary") == 0)
 				opts_out->format = COPY_FORMAT_BINARY;
+			else if (strcmp(fmt, "json") == 0)
+				opts_out->format = COPY_FORMAT_JSON;
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -701,21 +703,42 @@ ProcessCopyOptions(ParseState *pstate,
 	 * Check for incompatible options (must do these three before inserting
 	 * defaults)
 	 */
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->delim)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
-				 errmsg("cannot specify %s in BINARY mode", "DELIMITER")));
+	if (opts_out->delim)
+	{
+		if (opts_out->format == COPY_FORMAT_BINARY)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+			/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
+					errmsg("cannot specify %s in BINARY mode", "DELIMITER"));
+		else if (opts_out->format == COPY_FORMAT_JSON)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("cannot specify %s in JSON mode", "DELIMITER"));
+	}
 
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->null_print)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("cannot specify %s in BINARY mode", "NULL")));
+	if (opts_out->null_print)
+	{
+		if (opts_out->format == COPY_FORMAT_BINARY)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("cannot specify %s in BINARY mode", "NULL"));
+		else if (opts_out->format == COPY_FORMAT_JSON)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("cannot specify %s in JSON mode", "NULL"));
+	}
 
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->default_print)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("cannot specify %s in BINARY mode", "DEFAULT")));
+	if (opts_out->default_print)
+	{
+		if (opts_out->format == COPY_FORMAT_BINARY)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("cannot specify %s in BINARY mode", "DEFAULT"));
+		else if (opts_out->format == COPY_FORMAT_JSON)
+			ereport(ERROR,
+					errcode(ERRCODE_SYNTAX_ERROR),
+					errmsg("cannot specify %s in JSON mode", "DEFAULT"));
+	}
 
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
@@ -781,11 +804,18 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->header_line != COPY_HEADER_FALSE)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
-				 errmsg("cannot specify %s in BINARY mode", "HEADER")));
+	if (opts_out->header_line != COPY_HEADER_FALSE)
+	{
+		if (opts_out->format == COPY_FORMAT_BINARY)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
+					errmsg("cannot specify %s in BINARY mode", "HEADER"));
+		else if(opts_out->format == COPY_FORMAT_JSON)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot specify %s in JSON mode", "HEADER"));
+	}
 
 	/* Check quote */
 	if (opts_out->format != COPY_FORMAT_CSV && opts_out->quote != NULL)
@@ -889,6 +919,12 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY %s cannot be used with %s", "FREEZE",
 						"COPY TO")));
 
index e990343bab0..13eb14debbd 100644

+/* json format */
@@ -180,12 +191,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 	else if (opts->format == COPY_FORMAT_BINARY)
 
 	/* default is text */

 
 /*

+	 * If COPY TO source data come from query rather than plain table, we need
@@ -397,9 +445,21 @@ SendCopyBegin(CopyToState cstate)
 
@@ -499,7 +559,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
index db43034b9db..48e2242327e 100644
@@ -3528,6 +3528,10 @@ copy_opt_item:
@@ -3610,6 +3614,10 @@ copy_generic_opt_elem:
 
 copy_generic_opt_arg:
index e9d370cb3da..e517470bbc7 100644

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 1f2ca946fc5..16db5373c5f 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3344,8 +3344,10 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH(Copy_to_options);
 
 	/* Complete COPY <sth> FROM|TO filename WITH (FORMAT */
-	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAny, "WITH", "(", "FORMAT"))
+	else if (Matches("COPY|\\copy", MatchAny, "FROM", MatchAny, "WITH", "(", "FORMAT"))
 		COMPLETE_WITH("binary", "csv", "text");
+	else if (Matches("COPY|\\copy", MatchAny, "TO", MatchAny, "WITH", "(", "FORMAT"))
+		COMPLETE_WITH("binary", "csv", "text", "json");
 
 	/* Complete COPY <sth> FROM filename WITH (ON_ERROR */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM", MatchAny, "WITH", "(", "ON_ERROR"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 686653233b2..85aedc267d6 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -56,6 +56,7 @@ typedef enum CopyFormat
 	COPY_FORMAT_TEXT = 0,
 	COPY_FORMAT_BINARY,
 	COPY_FORMAT_CSV,
+	COPY_FORMAT_JSON,
 } CopyFormat;
 
 /*
 
index ac66eb55aee..0fc6e84352c 100644
@@ -73,6 +73,82 @@ copy copytest3 to stdout csv header;
+copy copytest to stdout (format json, header 1);
index a1316c73bac..071986d427a 100644

+copy copytest to stdout (format json, header 1);
index e6f2e93b2d6..374b40d14de 100644
@@ -515,6 +515,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.34.1

From 1b30cb9b34b770cebc0bb20af867baec2f72aedb Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 30 Jul 2025 16:48:56 +0800
Subject: [PATCH v18 1/3] introduce CopyFormat refactor CopyFormatOptions

Currently, COPY command format is determined by two booleans, binary and
csv_mode, within CopyFormatOptions. This approach, while functional, isn't ideal
for future expansion.

To simplify adding new formats, we've introduced an enum CopyFormat.  This makes
the code cleaner and more maintainable, allowing for easier integration of
additional formats down the line.

The CopyFormat enum was originally contributed by Joel Jacobson
[email-masked], later refactored by Jian He to address various issues.

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 src/backend/commands/copy.c          | 50 +++++++++++++++-------------
 src/backend/commands/copyfrom.c      |  6 ++--
 src/backend/commands/copyfromparse.c |  7 ++--
 src/backend/commands/copyto.c        |  8 ++---
 src/include/commands/copy.h          | 13 ++++++--
 5 files changed, 48 insertions(+), 36 deletions(-)

index fae9c41db65..68f69cfb9df 100644

@@ -535,11 +537,11 @@ ProcessCopyOptions(ParseState *pstate,
@@ -699,31 +701,31 @@ ProcessCopyOptions(ParseState *pstate,

 
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
-		opts_out->delim = opts_out->csv_mode ? "," : "\t";
+		opts_out->delim = (opts_out->format == COPY_FORMAT_CSV) ? "," : "\t";
 
 	if (!opts_out->null_print)
-		opts_out->null_print = opts_out->csv_mode ? "" : "\\N";
+		opts_out->null_print = (opts_out->format == COPY_FORMAT_CSV) ? "" : "\\N";
 	opts_out->null_print_len = strlen(opts_out->null_print);
 
@@ -771,7 +773,7 @@ ProcessCopyOptions(ParseState *pstate,
@@ -779,43 +781,43 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */
@@ -829,8 +831,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
@@ -845,8 +847,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
@@ -870,7 +872,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
@@ -906,7 +908,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
@@ -923,7 +925,7 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* default is text */

 /*

index 67b94b91cae..e990343bab0 100644
@@ -176,9 +176,9 @@ static const CopyToRoutine CopyToRoutineBinary = {
 
 	/* default is text */
@@ -215,7 +215,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

@@ -392,7 +392,7 @@ SendCopyBegin(CopyToState cstate)
 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 541176e1980..686653233b2 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -48,6 +48,16 @@ typedef enum CopyLogVerbosityChoice
 	COPY_LOG_VERBOSITY_VERBOSE, /* logs additional messages */
 } CopyLogVerbosityChoice;
 
+/*
@@ -58,9 +68,8 @@ typedef struct CopyFormatOptions

---

From: jian he <[email-masked]>
Date: Wed, 1 Oct 2025 14:16:42 +0800

> v18-0002, v18-0003 is refactoring based on prior patch.

hi.
v19 attached, same as v18.
repost it so that CFbot can pick up the latest patchset.
From 3869884bd47aaf681cc3c2bf96fe59d11069155c Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sun, 10 Aug 2025 23:13:38 +0800
Subject: [PATCH v19 2/3] json format for COPY TO

 
 
      <note>

 
 
 	/* Check header */
 
 	/* Check quote */

 
+/* json format */
 
 	/* default is text */

 
 /*

 
 
 /*
index f1def67ac7c..664b0483dbd 100644
@@ -3530,6 +3530,10 @@ copy_opt_item:
@@ -3612,6 +3616,10 @@ copy_generic_opt_elem:
 
 copy_generic_opt_arg:

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 6176741d20b..15fe7b37b0e 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3347,8 +3347,10 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH(Copy_to_options);

 
 /*

 
index 37f26f6c6b7..d85c2ec3c70 100644

From 2abacfaebc0fd5a37a3b797df92c3b3a85761afa Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 30 Jul 2025 19:50:41 +0800
Subject: [PATCH v19 3/3] Add option force_array for COPY JSON FORMAT

 
+   <varlistentry>

 
 	CopyFormatOptions opts;
 
 /* binary format */

 /*

 
index 15fe7b37b0e..a42fb6c0740 100644
@@ -1222,7 +1222,7 @@ Copy_common_options, "DEFAULT", "FORCE_NOT_NULL", "FORCE_NULL", "FREEZE", \
 
 /* COPY TO options */
 
 /*
 
+--Error

From 6c3e515ce84bdba4e0c96f46d8d5543481d3e1ca Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 30 Jul 2025 16:48:56 +0800
Subject: [PATCH v19 1/3] introduce CopyFormat refactor CopyFormatOptions

 

 

 
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

index 12781963b4f..ba31b227d5f 100644
 
 	/* default is text */

 /*

 
 	/* default is text */

 
 
+/*

---

From: jian he <[email-masked]>
Date: Mon, 10 Nov 2025 08:53:02 +0800

hi.

new patch attached, rebase only.
From 97e63d2b7de1fef820305b279d9e5602c82dab53 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 10 Nov 2025 08:39:36 +0800
Subject: [PATCH v20 1/3] introduce CopyFormat refactor CopyFormatOptions

 6 files changed, 49 insertions(+), 36 deletions(-)

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 28e878c3688..d674ada98e4 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -564,6 +564,8 @@ ProcessCopyOptions(ParseState *pstate,
 		opts_out = (CopyFormatOptions *) palloc0(sizeof(CopyFormatOptions));

@@ -578,11 +580,11 @@ ProcessCopyOptions(ParseState *pstate,
@@ -742,31 +744,31 @@ ProcessCopyOptions(ParseState *pstate,

 

@@ -814,7 +816,7 @@ ProcessCopyOptions(ParseState *pstate,
@@ -822,43 +824,43 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */
@@ -872,8 +874,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
@@ -888,8 +890,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
@@ -913,7 +915,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
@@ -949,7 +951,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
@@ -966,7 +968,7 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* default is text */

 /*

index cef452584e5..c97f0460b3e 100644
@@ -181,9 +181,9 @@ static const CopyToRoutine CopyToRoutineBinary = {
 
 	/* default is text */
@@ -220,7 +220,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

@@ -397,7 +397,7 @@ SendCopyBegin(CopyToState cstate)

+/*
index 432509277c9..256b5000af4 100644
@@ -516,6 +516,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.34.1

From e42e36118f73fa1a98f698031e3f1f7cbb9150cf Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 30 Jul 2025 19:50:41 +0800
Subject: [PATCH v20 3/3] Add option force_array for COPY JSON FORMAT

index 2d6d6802cbd..d8d9fb173b4 100644
 
+   <varlistentry>
index 0ec9b22d20f..6f9ae3fbfd7 100644
@@ -557,6 +557,7 @@ ProcessCopyOptions(ParseState *pstate,
 
@@ -713,6 +714,13 @@ ProcessCopyOptions(ParseState *pstate,
@@ -968,6 +976,11 @@ ProcessCopyOptions(ParseState *pstate,
 
index accf34e1a60..b58c5bdf987 100644
@@ -86,6 +86,10 @@ typedef struct CopyToStateData
 
 	CopyFormatOptions opts;
@@ -133,6 +137,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
@@ -177,7 +182,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 
 /* binary format */
@@ -243,6 +248,16 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

 /*
@@ -354,11 +369,31 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	result = makeStringInfo();
 	composite_to_json(rowdata, result, false);

 
index 0fd06a31201..e550aa38a25 100644
@@ -1232,7 +1232,7 @@ Copy_common_options, "DEFAULT", "FORCE_NOT_NULL", "FORCE_NULL", "FREEZE", \
 
 /* COPY TO options */
 
 /*
index 10333357d68..8becc70ee7a 100644
index 80799e2ead9..6a14cfc6e68 100644
 
+--Error

From 089630f0f4706b31c4c886d033e15ad20761dd6d Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 10 Nov 2025 08:40:26 +0800
Subject: [PATCH v20 2/3] json format for COPY TO

 10 files changed, 268 insertions(+), 34 deletions(-)

index fdc24b36bb8..2d6d6802cbd 100644

      <note>
index d674ada98e4..0ec9b22d20f 100644
@@ -585,6 +585,8 @@ ProcessCopyOptions(ParseState *pstate,
@@ -744,21 +746,42 @@ ProcessCopyOptions(ParseState *pstate,

 
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
@@ -824,11 +847,18 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
 
 	/* Check quote */
 	if (opts_out->format != COPY_FORMAT_CSV && opts_out->quote != NULL)
@@ -932,6 +962,12 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY %s cannot be used with %s", "FREEZE",
 						"COPY TO")));
 
index c97f0460b3e..accf34e1a60 100644
@@ -26,6 +26,7 @@
@@ -33,6 +34,7 @@
@@ -130,6 +132,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -149,7 +152,7 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 
@@ -169,6 +172,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
@@ -185,12 +196,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 
 	/* default is text */
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -209,6 +222,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -231,7 +246,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 }
 
 /*
@@ -304,13 +319,46 @@ CopyToTextLikeOneRow(CopyToState cstate,

@@ -402,9 +450,21 @@ SendCopyBegin(CopyToState cstate)
 
@@ -504,7 +564,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
index 57fe0186547..7cbdadc98ac 100644
@@ -3557,6 +3557,10 @@ copy_opt_item:
@@ -3639,6 +3643,10 @@ copy_generic_opt_elem:
 
 copy_generic_opt_arg:
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 06dd62f0008..647adafd227 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -86,8 +86,6 @@ typedef struct JsonAggState
 	JsonUniqueBuilderState unique_check;
 } JsonAggState;
 
-static void composite_to_json(Datum composite, StringInfo result,
-							  bool use_line_feeds);
 static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
 							  const Datum *vals, const bool *nulls, int *valcount,
 							  JsonTypeCategory tcategory, Oid outfuncoid,
@@ -517,8 +515,9 @@ array_to_json_internal(Datum array, StringInfo result, bool use_line_feeds)
 
 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 316a2dafbf1..0fd06a31201 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3376,7 +3376,7 @@ match_previous_words(int pattern_id,
 	/* Complete COPY <sth> FROM|TO [PROGRAM] <sth> WITH (FORMAT */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM|TO", MatchAnyExcept("PROGRAM"), "WITH", "(", "FORMAT") ||
 			 Matches("COPY|\\copy", MatchAny, "FROM|TO", "PROGRAM", MatchAny, "WITH", "(", "FORMAT"))
-		COMPLETE_WITH("binary", "csv", "text");
+		COMPLETE_WITH("binary", "csv", "text", "json");
 
 	/* Complete COPY <sth> FROM [PROGRAM] filename WITH (ON_ERROR */
 	else if (Matches("COPY|\\copy", MatchAny, "FROM", MatchAnyExcept("PROGRAM"), "WITH", "(", "ON_ERROR") ||
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 686653233b2..85aedc267d6 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -56,6 +56,7 @@ typedef enum CopyFormat
 	COPY_FORMAT_TEXT = 0,
 	COPY_FORMAT_BINARY,
 	COPY_FORMAT_CSV,
+	COPY_FORMAT_JSON,
 } CopyFormat;
 
 /*
 
index 24e0f472f14..10333357d68 100644
index 676a8b342b5..80799e2ead9 100644

---

From: jian he <[email-masked]>
Date: Sat, 29 Nov 2025 10:46:35 +0800

hi.

https://commitfest.postgresql.org/patch/4716/
says need rebase.
turns out only copy.sgml has conflict.
it conflict with
https://git.postgresql.org/cgit/postgresql.git/commit/?id=e4018f891dec09ff95ac97e5b1a2307349aeeffa

So the rebase only needs to update copy.sgml.

--
jian
https://www.enterprisedb.com/
From 3ff9058b29e5410a976c1013484f55df27f132a5 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 10 Nov 2025 08:40:26 +0800
Subject: [PATCH v21 2/3] json format for COPY TO

index 53b0ea8f573..320f5f1edd4 100644

      <note>

 
 
 	/* Check header */
 
 	/* Check quote */

 
+/* json format */
 
 	/* default is text */

 
 /*

 
 
 /*
index c3a0a354a9c..dd23c075710 100644
 
 copy_generic_opt_arg:

 /*
index 20d7a65c614..2029b1930c8 100644
@@ -3377,7 +3377,7 @@ match_previous_words(int pattern_id,

 /*

 

From 93b28c6521d5ea6f7a4e901acf910f19e8ef6528 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sat, 29 Nov 2025 10:37:01 +0800
Subject: [PATCH v21 3/3] Add option force_array for COPY JSON FORMAT

index 320f5f1edd4..a274118b0fa 100644
 
+   <varlistentry id="sql-copy-params-force-array">
    <varlistentry id="sql-copy-params-force-quote">

 
 	CopyFormatOptions opts;
 
 /* binary format */

 /*

 
index 2029b1930c8..c25c3cdb72b 100644
 
 /* COPY TO options */
 
 /*
 
+--Error

From fbd5ef17532bc111e40d9352049fe9fd4e807aae Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 10 Nov 2025 08:39:36 +0800
Subject: [PATCH v21 1/3] introduce CopyFormat refactor CopyFormatOptions

 

 

 
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

 
 	/* default is text */
index a09e7fbace3..9cc5bb1cf5c 100644

 /*

 
 	/* default is text */

 
 
+/*
index cf3f6a7dafd..6d1f2d5bb3b 100644

---

From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 20:15:25 +0800

hi.

rebase only.

--
jian
https://www.enterprisedb.com/
From c47611ebcafd3e8f58f1b1698aff8289c99b5899 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:38:24 +0800
Subject: [PATCH v22 1/3] introduce CopyFormat refactor CopyFormatOptions

Currently, COPY command format is determined by two booleans (binary, csv_mode)
fields in CopyFormatOptions This approach, while functional, isn't ideal for
future other implement other format.

The CopyFormat enum was originally contributed by Joel Jacobson <[email-masked]>,
later refactored by Jian He to address various issues.

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 9c51384ab92..8d92c513fad 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -564,6 +564,8 @@ ProcessCopyOptions(ParseState *pstate,
 		opts_out = palloc0_object(CopyFormatOptions);

 

 

 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

index 25ee20b23db..0c73b0259c3 100644
 
 	/* default is text */
index 5868a7fa11f..a28e7ee3626 100644

 /*

index 4ab4a3893d5..880231ea6cd 100644
 
 	/* default is text */

 
index 43c2580539f..7be41d9da12 100644
 
+/*
index 3f3a888fd0e..03fae82f656 100644
@@ -527,6 +527,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.34.1

From 366db5fc956ea2436cc16f4dc7946411ffe0f2b3 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sat, 29 Nov 2025 10:37:01 +0800
Subject: [PATCH v22 3/3] Add option force_array for COPY JSON FORMAT

 
index 7860afe44da..c2b432a96eb 100644

index f3f257eaef2..a72bfed9814 100644
 
 	CopyFormatOptions opts;
 
 /* binary format */

 /*

 
index 37cb64d2b72..a610ef603f4 100644
 
 /* COPY TO options */
 
 /*
index fe85f02b110..b2a68fa6407 100644
 
+--Error

From 861cf905fcddece82a13aaff4b400992deb881f2 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:43:14 +0800
Subject: [PATCH v22 2/3] json format for COPY TO

 
 
      <note>
index 8d92c513fad..7860afe44da 100644

 
 
 	/* Check header */
 
 	/* Check quote */
 
index 880231ea6cd..f3f257eaef2 100644

+/* json format */
 
 	/* default is text */

 
 /*

 
 
 /*
index 713ee5c10a2..f70a465bb64 100644
@@ -3609,6 +3609,10 @@ copy_opt_item:
@@ -3691,6 +3695,10 @@ copy_generic_opt_elem:
 
 copy_generic_opt_arg:
index 78e84727fdc..eec6c5f5ea1 100644

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 8b91bc00062..37cb64d2b72 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3413,7 +3413,7 @@ match_previous_words(int pattern_id,
 
 			/* Complete COPY <sth> FROM|TO filename WITH (FORMAT */
 			else if (TailMatches("FORMAT"))
-				COMPLETE_WITH("binary", "csv", "text");
+				COMPLETE_WITH("binary", "csv", "text", "json");
 
 			/* Complete COPY <sth> FROM|TO filename WITH (FREEZE */
 			else if (TailMatches("FREEZE"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 7be41d9da12..fe85f02b110 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -56,6 +56,7 @@ typedef enum CopyFormat
 	COPY_FORMAT_TEXT = 0,
 	COPY_FORMAT_BINARY,
 	COPY_FORMAT_CSV,
+	COPY_FORMAT_JSON,
 } CopyFormat;
 
 /*
index f8cc52b1e78..2f4be40518d 100644

---

From: Andrew Dunstan <[email-masked]>
Date: Wed, 4 Mar 2026 10:51:14 -0500

On 2026-02-08 Su 10:48 PM, jian he wrote:
> On Sat, Feb 7, 2026 at 9:27 PM Junwang Zhao<[email-masked]> wrote:
>> Here are some comments on v23:
>>
>> 0001: The refactor looks straightforward to me. Introducing a format
>> field should make future extensions easier. One suggestion is that we
>> could add some helper macros around format, for example:
>>
>> #define IS_FORMAT_CSV(format) (format == COPY_FORMAT_CSV)
>> #define IS_FORMAT_TEXT_LIKE(format) \
>>      (format == COPY_FORMAT_TEXT || format == COPY_FORMAT_CSV)
>>
>> I think this would improve readability.
> Personally, I don't like marcos....
>
>> 0002: Since you have moved the `CopyFormat enum` into 0001, the
>> following commit msg should be rephrased.
>>
>> Can we add a function that converts CopyFormat to a string? Treating
>> CopyFormat as %s in error messages would make the code shorter.
>> However, I'm not sure whether this aligns with translation
>> conventions, correct me if I'm wrong.
>>
> I don’t think this is worth the added complexity.
> That said, I tried to simplify the code and changed it to:
>
>      if (opts_out->delim &&
>          (opts_out->format == COPY_FORMAT_BINARY ||
>           opts_out->format == COPY_FORMAT_JSON))
>          ereport(ERROR,
>                  errcode(ERRCODE_SYNTAX_ERROR),
>                  opts_out->format == COPY_FORMAT_BINARY
>                  ? errmsg("cannot specify %s in BINARY mode", "DELIMITER")
>                  : errmsg("cannot specify %s in JSON mode", "DELIMITER"));
>
>> I'd suggest rewording to `CSV, text and json ...`. The same applied to
>> other parts in this patch.
>>
> sure.
>
>> 0003: The commit message includes some changes(adapt the newly
>> introduced CopyToRoutine) that actually belong to 0002; it would be
>> better to remove them from this commit.
>>
> 0002 commit message:
> """
> This introduces the JSON format option for the COPY TO command, allowing users
> to export query results or table data directly as a single JSON object or a
> stream of JSON objects.
>
> The JSON format is currently supported only for COPY TO operations; it
> is not available for COPY FROM.
>
> JSON format is incompatible with some standard text/CSV parsing or
> formatting options,
> including:
> - HEADER
> - DEFAULT
> - NULL
> - DELIMITER
> - FORCE QUOTE / FORCE NOT NULL
>
> Regression tests covering valid JSON exports and error handling for
> incompatible options have been added to src/test/regress/sql/copy.sql.
> """
>
> 0003 commit message:
> """
> Add option force_array for COPY JSON FORMAT
> This adds the force_array option, which is available exclusively
> when using COPY TO with the JSON format.
>
> When enabled, this option wraps the output in a top-level JSON array
> (enclosed in square brackets with comma-separated elements), making the
> entire result a valid single JSON value. Without this option, the default
> behavior is to output a stream of independent JSON objects.
>
> Attempting to use this option with COPY FROM or with formats other than
> JSON will raise an error.
> """
>
>> can we do this:
>> if (cstate->opts.force_array)
>> {
>>      if (cstate->json_row_delim_needed)
>>          CopySendChar(cstate, ',');
>>      else
>>      {
>>          /* first row needs no delimiter */
>>          CopySendChar(cstate, ' ');
>>          cstate->json_row_delim_needed = true;
>>      }
>> }
>>
> good suggestion.
>
> If more people think WRAP_ARRAY is better than FORCE_ARRAY, we can
> switch to it accordingly.
> The change itself is quite straightforward.

I have reworked these. First I cleaned up a number of things in patches 
2 and 3 (Thanks, Claude for the summary):

Patch 2: json format for COPY TO

copy.c:
   - "json" → "JSON" in the COPY FROM rejection error message.

   copyto.c:
   1. TupleDesc setup runs once, not every row — Added 
json_tupledesc_ready flag; the 
memcpy/populate_compact_attribute/BlessTupleDesc block is now guarded by 
if (!cstate->json_tupledesc_ready).
   2. Comment rewritten — Old: "the slot's TupleDesc may change during 
query execution". New: explains BlessTupleDesc registers the RECORDOID 
descriptor so lookup_rowtype_tupdesc inside composite_to_json can
   find it.
   3. Eliminated per-row makeStringInfo() — Added StringInfoData 
json_buf to the struct, initialized once in CopyToTextLikeStart in 
copycontext. Each row does resetStringInfo instead of allocating a new
   StringInfo.
   4. Column list rejection added — Error: "column selection is not 
supported in JSON mode" when attnamelist != NIL.
   5. Improved SendCopyBegin comment — Old: "JSON format is always one 
non-binary column". New: explains each CopyData message contains one 
complete JSON object.

   Tests:
   6. Added copy copytest (style) to stdout (format json) to the 
error-case block.
   7. Added copyjsontype table test with json, jsonb columns — verifies 
values are embedded directly, not double-encoded. Covers json objects, 
scalars, arrays, nested objects, and nulls.

   Patch 3: Add option force_array

   copy.c:
   1. "json" → "JSON" in COPY FROM error (carried from patch 2).
   2. "can only used" → "can only be used" — grammar fix in FORCE_ARRAY 
error.

   copyto.c:
   3. Struct fields reorganized — JSON fields grouped under /* JSON 
format state */ comment with inline descriptions, instead of a 
standalone json_row_delim_needed with a vague comment.
   4. Block comment updated — Was "CSV, text and json formats share the 
same TextLike routines except for the one-row callback". Now correctly 
notes JSON has its own one-row and end callbacks.
   5. CopyToTextLikeEnd comment fixed — Was "text, CSV, and json", now 
"text and CSV" (JSON uses CopyToJsonEnd).
   6. Cleaner start callback — FORCE_ARRAY bracket emission moved inside 
the if (format == JSON) block after json_buf init, instead of a separate 
top-level conditional.
   7. Inherits all patch 2 fixes — TupleDesc guard, reusable json_buf, 
improved comments, column list rejection.

   Tests:
   8. --Error → -- should fail: force_array requires json format; --ok → 
-- force_array variants.
   9. copyjsontype test carried through from patch 2.

Then I reworked the way this works. In order to support column lists 
with JSON output, we need to deal with individual columns instead of 
whole records. This involved quite a number of changes, as can be seen 
in patch 4. This involved exporting a new small function from json.c.

The result is a lot cleaner, I believe, and in my benchmarking is faster 
by a factor of almost 2.

cheers

andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com

---

From: Andrew Dunstan <[email-masked]>
Date: Thu, 5 Mar 2026 15:49:55 -0500

On 2026-03-05 Th 1:06 PM, Joe Conway wrote:
>> whole records. This involved quite a number of changes, as can be 
>> seen in patch 4. This involved exporting a new small function from 
>> json.c.
>>
>> The result is a lot cleaner, I believe, and in my benchmarking is 
>> faster by a factor of almost 2.
>
> Andrew,
>
> I don't see the actual patches. Did I miss it somewhere?

Nope. Bad hair day apparently.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com
From b50c26e9e2a76001315fb3e5000f2d33e254c741 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:38:24 +0800
Subject: [PATCH v25 1/4] introduce CopyFormat refactor CopyFormatOptions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 63b86802ba2..2f46be516f2 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -576,6 +576,8 @@ ProcessCopyOptions(ParseState *pstate,
 		opts_out = palloc0_object(CopyFormatOptions);

@@ -590,11 +592,11 @@ ProcessCopyOptions(ParseState *pstate,
@@ -754,31 +756,31 @@ ProcessCopyOptions(ParseState *pstate,

 

@@ -826,7 +828,7 @@ ProcessCopyOptions(ParseState *pstate,
@@ -834,43 +836,43 @@ ProcessCopyOptions(ParseState *pstate,
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */
@@ -884,8 +886,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY FROM")));
 
@@ -900,8 +902,8 @@ ProcessCopyOptions(ParseState *pstate,
 						"COPY TO")));
 
 	/* Check force_null */
@@ -925,7 +927,7 @@ ProcessCopyOptions(ParseState *pstate,
 						"NULL")));
 
@@ -961,7 +963,7 @@ ProcessCopyOptions(ParseState *pstate,
 							"DEFAULT")));
 
@@ -978,7 +980,7 @@ ProcessCopyOptions(ParseState *pstate,
index 2f42f55e229..4d927410159 100644
@@ -156,9 +156,9 @@ static const CopyFromRoutine CopyFromRoutineBinary = {
 
 	/* default is text */
@@ -262,7 +262,7 @@ CopyFromErrorCallback(void *arg)
 				   cstate->cur_relname);
 		return;
 	}
-	if (cstate->opts.binary)
+	if (cstate->opts.format == COPY_FORMAT_BINARY)
 	{
 		/* can't usefully display the data */
 		if (cstate->cur_attname)
diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index fbd13353efc..c366874bd95 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -172,7 +172,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 {
 	StringInfoData buf;
 	int			natts = list_length(cstate->attnumlist);
-	int16		format = (cstate->opts.binary ? 1 : 0);
+	int16		format = (cstate->opts.format == COPY_FORMAT_BINARY ? 1 : 0);
 	int			i;
 
@@ -750,7 +750,7 @@ bool
 
 /*
@@ -777,7 +777,8 @@ NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields
 	bool		done = false;

index 9ceeff6d99e..0325a16f82a 100644
 
 	/* default is text */

 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 877202af67b..2430fb0b2e5 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -49,6 +49,16 @@ typedef enum CopyLogVerbosityChoice
 	COPY_LOG_VERBOSITY_VERBOSE, /* logs additional messages */
 } CopyLogVerbosityChoice;
 
+/*
@@ -59,9 +69,8 @@ typedef struct CopyFormatOptions
index 77e3c04144e..8399be97fd5 100644
@@ -528,6 +528,7 @@ ConversionLocation
 ConvertRowtypeExpr
 CookedConstraint
 CopyDest
+CopyFormat
 CopyFormatOptions
 CopyFromRoutine
 CopyFromState
-- 
2.43.0

From 285be0d7935b5505b6cc1509742f3fc87e19ea09 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 9 Feb 2026 11:00:06 +0800
Subject: [PATCH v25 2/4] json format for COPY TO

---
 doc/src/sgml/ref/copy.sgml         |  13 ++--
 src/backend/commands/copy.c        |  49 ++++++++++----
 src/backend/commands/copyto.c      | 101 ++++++++++++++++++++++++++---
 src/backend/parser/gram.y          |   8 +++
 src/backend/utils/adt/json.c       |   5 +-
 src/bin/psql/tab-complete.in.c     |   2 +-
 src/include/commands/copy.h        |   1 +
 src/include/utils/json.h           |   2 +
 src/test/regress/expected/copy.out |  78 ++++++++++++++++++++++
 src/test/regress/sql/copy.sql      |  48 ++++++++++++++
 10 files changed, 278 insertions(+), 29 deletions(-)

index 0ad890ef95f..75f55bbf6f8 100644

      <note>
@@ -303,7 +308,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       is found in the input file, the default value of the corresponding column
       will be used.
       This option is allowed only in <command>COPY FROM</command>, and only when
-      not using <literal>binary</literal> format.
+      not using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
@@ -330,7 +335,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       <command>COPY FROM</command> commands.
      </para>
      <para>
-      This option is not allowed when using <literal>binary</literal> format.
+      This option is not allowed when using <literal>binary</literal> or <literal>json</literal> format.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 2f46be516f2..29c121c7f08 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -597,6 +597,8 @@ ProcessCopyOptions(ParseState *pstate,
 				opts_out->format = COPY_FORMAT_CSV;
 			else if (strcmp(fmt, "binary") == 0)
 				opts_out->format = COPY_FORMAT_BINARY;
+			else if (strcmp(fmt, "json") == 0)
+				opts_out->format = COPY_FORMAT_JSON;
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -756,21 +758,32 @@ ProcessCopyOptions(ParseState *pstate,
 	 * Check for incompatible options (must do these three before inserting
 	 * defaults)
 	 */
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->delim)
+	if (opts_out->delim &&
+		(opts_out->format == COPY_FORMAT_BINARY ||
+		 opts_out->format == COPY_FORMAT_JSON))
 		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
-				 errmsg("cannot specify %s in BINARY mode", "DELIMITER")));
+				errcode(ERRCODE_SYNTAX_ERROR),
+				opts_out->format == COPY_FORMAT_BINARY
+				? errmsg("cannot specify %s in BINARY mode", "DELIMITER")
+				: errmsg("cannot specify %s in JSON mode", "DELIMITER"));
 
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->null_print)
+	if (opts_out->null_print &&
+		(opts_out->format == COPY_FORMAT_BINARY ||
+		 opts_out->format == COPY_FORMAT_JSON))
 		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("cannot specify %s in BINARY mode", "NULL")));
+				errcode(ERRCODE_SYNTAX_ERROR),
+				opts_out->format == COPY_FORMAT_BINARY
+				? errmsg("cannot specify %s in BINARY mode", "NULL")
+				: errmsg("cannot specify %s in JSON mode", "NULL"));
 
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->default_print)
+	if (opts_out->default_print &&
+		(opts_out->format == COPY_FORMAT_BINARY ||
+		 opts_out->format == COPY_FORMAT_JSON))
 		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("cannot specify %s in BINARY mode", "DEFAULT")));
+				errcode(ERRCODE_SYNTAX_ERROR),
+				opts_out->format == COPY_FORMAT_BINARY
+				? errmsg("cannot specify %s in BINARY mode", "DEFAULT")
+				: errmsg("cannot specify %s in JSON mode", "DEFAULT"));
 
 	/* Set defaults for omitted options */
 	if (!opts_out->delim)
@@ -836,11 +849,15 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
-	if (opts_out->format == COPY_FORMAT_BINARY && opts_out->header_line != COPY_HEADER_FALSE)
+	if (opts_out->header_line != COPY_HEADER_FALSE &&
+		(opts_out->format == COPY_FORMAT_BINARY ||
+		 opts_out->format == COPY_FORMAT_JSON))
 		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
-				 errmsg("cannot specify %s in BINARY mode", "HEADER")));
+				opts_out->format == COPY_FORMAT_BINARY
+				? errmsg("cannot specify %s in BINARY mode", "HEADER")
+				: errmsg("cannot specify %s in JSON mode", "HEADER"));
 
 	/* Check quote */
 	if (opts_out->format != COPY_FORMAT_CSV && opts_out->quote != NULL)
@@ -944,6 +961,12 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY %s cannot be used with %s", "FREEZE",
 						"COPY TO")));
 
+	/* Check json format */
+	if (opts_out->format == COPY_FORMAT_JSON && is_from)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s mode cannot be used with %s", "JSON", "COPY FROM"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 0325a16f82a..96605079eeb 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -26,6 +26,7 @@
 #include "executor/execdesc.h"
 #include "executor/executor.h"
 #include "executor/tuptable.h"
+#include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -33,6 +34,7 @@
 #include "pgstat.h"
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
+#include "utils/json.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -84,6 +86,11 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+
+	/* JSON format state */
+	bool		json_tupledesc_ready;	/* TupleDesc setup done for JSON */
+	StringInfoData json_buf;	/* reusable buffer for JSON output */
+
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -130,6 +137,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -149,7 +157,7 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 /*
  * COPY TO routines for built-in formats.
  *
- * CSV and text formats share the same TextLike routines except for the
+ * CSV, text and json formats share the same TextLike routines except for the
  * one-row callback.
  */
 
@@ -169,6 +177,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
@@ -185,12 +201,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 
 	/* default is text */
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -209,6 +227,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -228,10 +248,21 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 
 		CopySendTextLikeEndOfRow(cstate);
 	}
+
+	/* JSON-specific initialization */
+	if (cstate->opts.format == COPY_FORMAT_JSON)
+	{
+		MemoryContext oldcxt;
+
+		/* Allocate reusable JSON output buffer in long-lived context */
+		oldcxt = MemoryContextSwitchTo(cstate->copycontext);
+		initStringInfo(&cstate->json_buf);
+		MemoryContextSwitchTo(oldcxt);
+	}
 }
 
 /*
@@ -304,13 +335,47 @@ CopyToTextLikeOneRow(CopyToState cstate,

+/* Implementation of per-row callback for json format */
+static void
+CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
+{
+	Datum		rowdata;
+
+	/*
+	 * For query-based COPY, copy the query's TupleDesc attributes into the
+	 * slot's TupleDesc once.  BlessTupleDesc registers the RECORDOID
+	 * descriptor so that lookup_rowtype_tupdesc inside composite_to_json can
+	 * find it.
+	 */
+	if (!cstate->rel && !cstate->json_tupledesc_ready)
+	{
+		memcpy(TupleDescAttr(slot->tts_tupleDescriptor, 0),
+			   TupleDescAttr(cstate->queryDesc->tupDesc, 0),
+			   cstate->queryDesc->tupDesc->natts * sizeof(FormData_pg_attribute));
+
+		for (int i = 0; i < cstate->queryDesc->tupDesc->natts; i++)
+			populate_compact_attribute(slot->tts_tupleDescriptor, i);
+
+		BlessTupleDesc(slot->tts_tupleDescriptor);
+		cstate->json_tupledesc_ready = true;
+	}
+
+	rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	resetStringInfo(&cstate->json_buf);
+	composite_to_json(rowdata, &cstate->json_buf, false);
+
+	CopySendData(cstate, cstate->json_buf.data, cstate->json_buf.len);
+
+	CopySendTextLikeEndOfRow(cstate);
+}
+
 /*
  * Implementation of the start callback for binary format. Send a header
  * for a binary copy.
@@ -402,9 +467,23 @@ SendCopyBegin(CopyToState cstate)
 
 	pq_beginmessage(&buf, PqMsg_CopyOutResponse);
 	pq_sendbyte(&buf, format);	/* overall format */
-	pq_sendint16(&buf, natts);
-	for (i = 0; i < natts; i++)
-		pq_sendint16(&buf, format); /* per-column formats */
+	if (cstate->opts.format != COPY_FORMAT_JSON)
+	{
+		pq_sendint16(&buf, natts);
+		for (i = 0; i < natts; i++)
+			pq_sendint16(&buf, format); /* per-column formats */
+	}
+	else
+	{
+		/*
+		 * For JSON format, report one text-format column.  Each CopyData
+		 * message contains one complete JSON object, not individual column
+		 * values, so the per-column count is always 1.
+		 */
+		pq_sendint16(&buf, 1);
+		pq_sendint16(&buf, 0);
+	}
+
 	pq_endmessage(&buf);
 	cstate->copy_dest = COPY_FRONTEND;
 }
@@ -506,7 +585,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
- * Wrapper function of CopySendEndOfRow for text and CSV formats. Sends the
+ * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the
  * line termination and do common appropriate things for the end of row.
  */
 static inline void
@@ -890,6 +969,12 @@ BeginCopyTo(ParseState *pstate,
 	/* Generate or convert list of attributes to process */
 	cstate->attnumlist = CopyGetAttnums(tupDesc, cstate->rel, attnamelist);
 
+	/* JSON outputs whole rows; a column list doesn't make sense */
+	if (cstate->opts.format == COPY_FORMAT_JSON && attnamelist != NIL)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("column selection is not supported in JSON mode")));
+
 	num_phys_attrs = tupDesc->natts;
 
 	/* Convert FORCE_QUOTE name list to per-column flags, check validity */
index c567252acc4..db98f2d91bf 100644
 
 copy_generic_opt_arg:
index 0b161398465..f609d7b9417 100644

 /*
  * Turn a composite / record into JSON.
+ * Exported so COPY TO can use it.
  */
-static void
+void
 composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 {
 	HeapTupleHeader td;
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 905c076763c..d257837b0c5 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3425,7 +3425,7 @@ match_previous_words(int pattern_id,

 			/* Complete COPY <sth> FROM|TO filename WITH (FREEZE */
 			else if (TailMatches("FREEZE"))
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 2430fb0b2e5..2b5bef6738e 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -57,6 +57,7 @@ typedef enum CopyFormat
 	COPY_FORMAT_TEXT = 0,
 	COPY_FORMAT_BINARY,
 	COPY_FORMAT_CSV,
+	COPY_FORMAT_JSON,
 } CopyFormat;
 
 /*
 
index d0d563e0fa8..4ea658a45de 100644
@@ -73,6 +73,84 @@ copy copytest3 to stdout csv header;
+ERROR:  COPY JSON mode cannot be used with COPY FROM
+copy copytest (style) to stdout (format json);
+ERROR:  column selection is not supported in JSON mode
index 65cbdaf7f3e..c558eba202a 100644
@@ -82,6 +82,54 @@ this is just a line full of junk that would error out if parsed

+copy copytest (style) to stdout (format json);
2.43.0

From 312dedc0a3aea1833bb992f096121db4086fd075 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 9 Feb 2026 11:14:15 +0800
Subject: [PATCH v25 3/4] Add option force_array for COPY JSON FORMAT

---
 doc/src/sgml/ref/copy.sgml         | 30 +++++++++++++++++++++
 src/backend/commands/copy.c        | 13 +++++++++
 src/backend/commands/copyto.c      | 43 +++++++++++++++++++++++++++---
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 23 ++++++++++++++++
 src/test/regress/sql/copy.sql      |  8 ++++++
 7 files changed, 115 insertions(+), 5 deletions(-)

index 75f55bbf6f8..a79587f7613 100644
 
@@ -1103,6 +1117,22 @@ COPY country TO STDOUT (DELIMITER '|');
 </programlisting>
   </para>
 
+<para>
+   When the <literal>FORCE_ARRAY</literal> option is enabled,
+   the entire output is wrapped in a single JSON array with rows separated by commas:
+<programlisting>
+COPY (SELECT * FROM (VALUES(1),(2)) val(id)) TO STDOUT  (FORMAT JSON, FORCE_ARRAY);
+</programlisting>
+The output is as follows:
+<screen>
+[
+ {"id":1}
+,{"id":2}
+]
+</screen>
+</para>
+
+
   <para>
    To copy data from a file into the <literal>country</literal> table:
 <programlisting>
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 29c121c7f08..84254d46a67 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -569,6 +569,7 @@ ProcessCopyOptions(ParseState *pstate,
 	bool		on_error_specified = false;
 	bool		log_verbosity_specified = false;
 	bool		reject_limit_specified = false;
+	bool		force_array_specified = false;
 	ListCell   *option;
 
 	/* Support external use for option sanity checking */
@@ -725,6 +726,13 @@ ProcessCopyOptions(ParseState *pstate,
 								defel->defname),
 						 parser_errposition(pstate, defel->location)));
 		}
+		else if (strcmp(defel->defname, "force_array") == 0)
+		{
+			if (force_array_specified)
+				errorConflictingDefElem(defel, pstate);
+			force_array_specified = true;
+			opts_out->force_array = defGetBoolean(defel);
+		}
 		else if (strcmp(defel->defname, "on_error") == 0)
 		{
 			if (on_error_specified)
@@ -967,6 +975,11 @@ ProcessCopyOptions(ParseState *pstate,
 				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				errmsg("COPY %s mode cannot be used with %s", "JSON", "COPY FROM"));
 
+				errmsg("COPY %s can only be used with JSON mode", "FORCE_ARRAY"));
index 96605079eeb..a7615cc34ec 100644
 
 	/* JSON format state */
+	bool		json_row_delim_needed;	/* need delimiter before next row */
 	bool		json_tupledesc_ready;	/* TupleDesc setup done for JSON */
 	StringInfoData json_buf;	/* reusable buffer for JSON output */
 
@@ -138,6 +139,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
 static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
+static void CopyToJsonEnd(CopyToState cstate);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -157,8 +159,9 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 /*
  * COPY TO routines for built-in formats.
  *
- * CSV, text and json formats share the same TextLike routines except for the
- * one-row callback.
+ * Text and CSV formats share the same TextLike routines except for the
+ * one-row callback.  JSON shares the start and outfunc callbacks with
+ * text/CSV, but has its own one-row and end callbacks.
  */
 
 /* text format */
@@ -182,7 +185,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 
 /* binary format */
@@ -258,6 +261,15 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		oldcxt = MemoryContextSwitchTo(cstate->copycontext);
 		initStringInfo(&cstate->json_buf);
 		MemoryContextSwitchTo(oldcxt);
+
+		/*
+		 * If FORCE_ARRAY has been specified, send the opening bracket.
+		 */
+		if (cstate->opts.force_array)
+		{
+			CopySendChar(cstate, '[');
+			CopySendTextLikeEndOfRow(cstate);
+		}
 	}
 }
 
@@ -335,7 +347,7 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }
 
-/* Implementation of the end callback for text, CSV, and json formats */
+/* Implementation of the end callback for text and CSV formats */
 static void
 CopyToTextLikeEnd(CopyToState cstate)
 {
@@ -371,11 +383,34 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	resetStringInfo(&cstate->json_buf);
 	composite_to_json(rowdata, &cstate->json_buf, false);
 
+	if (cstate->opts.force_array)
+	{
+		if (cstate->json_row_delim_needed)
+			CopySendChar(cstate, ',');
+		else
+		{
+			/* first row needs no delimiter */
+			CopySendChar(cstate, ' ');
+			cstate->json_row_delim_needed = true;
+		}
+	}
+
 	CopySendData(cstate, cstate->json_buf.data, cstate->json_buf.len);

index d257837b0c5..76d3258e92b 100644
 
 /* COPY TO options */
 
 /*
  * These object types were introduced later than our support cutoff of
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 2b5bef6738e..abecfe51098 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -88,6 +88,7 @@ typedef struct CopyFormatOptions
 	List	   *force_notnull;	/* list of column names */
 	bool		force_notnull_all;	/* FORCE_NOT_NULL *? */
 	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+	bool		force_array;	/* add JSON array decorations */
 	List	   *force_null;		/* list of column names */
 	bool		force_null_all; /* FORCE_NULL *? */
 	bool	   *force_null_flags;	/* per-column CSV FN flags */
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 4ea658a45de..a7e88b711d7 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -114,6 +114,29 @@ ERROR:  COPY JSON mode cannot be used with COPY FROM
 copy copytest (style) to stdout (format json);
 ERROR:  column selection is not supported in JSON mode
 -- all of the above should yield error
+-- should fail: force_array requires json format
+copy copytest to stdout (format csv, force_array true);
+ERROR:  COPY FORCE_ARRAY can only be used with JSON mode
+-- force_array variants
+copy copytest to stdout (format json, force_array);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array false);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index c558eba202a..ae202fc5e8d 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -102,6 +102,14 @@ copy copytest from stdin(format json);
 copy copytest (style) to stdout (format json);
 -- all of the above should yield error
 
+-- should fail: force_array requires json format
+-- force_array variants
2.43.0

From d043adcbb2032eb2c1218df99992008838f2e200 Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <[email-masked]>
Date: Wed, 4 Mar 2026 09:40:10 -0500
Subject: [PATCH v25 4/4] COPY TO JSON: build JSON per-column, support column
 lists

Rework CopyToJsonOneRow to iterate attnumlist and build JSON objects
column-by-column using datum_to_json_append, instead of converting the
whole row via ExecFetchSlotHeapTupleDatum + composite_to_json.

This has several benefits:
- Column lists now work with JSON format (previously rejected)
- Per-column JSON type categorization is done once at startup rather
  than on every row (composite_to_json called json_categorize_type
  per column per row)
- The TupleDesc memcpy/BlessTupleDesc hack for query-based COPY is
  eliminated entirely
- Pre-escaped column key strings avoid repeated escape_json calls

Add CopyToJsonStart (pre-computes escaped key strings and json_buf),
CopyToJsonOutFunc (calls json_categorize_type once per column), and
export datum_to_json_append from json.c for efficient append-to-
StringInfo JSON serialization.
---
 src/backend/commands/copyto.c      | 159 ++++++++++++++++++-----------
 src/backend/utils/adt/json.c       |  14 +++
 src/include/utils/jsonfuncs.h      |   2 +
 src/test/regress/expected/copy.out |   8 +-
 src/test/regress/sql/copy.sql      |   4 +-
 5 files changed, 126 insertions(+), 61 deletions(-)

diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index a7615cc34ec..9502c910b43 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -26,7 +26,6 @@
 #include "executor/execdesc.h"
 #include "executor/executor.h"
 #include "executor/tuptable.h"
-#include "funcapi.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "mb/pg_wchar.h"
@@ -35,6 +34,7 @@
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
 #include "utils/json.h"
+#include "utils/jsonfuncs.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -89,8 +89,10 @@ typedef struct CopyToStateData
 
 	/* JSON format state */
 	bool		json_row_delim_needed;	/* need delimiter before next row */
-	bool		json_tupledesc_ready;	/* TupleDesc setup done for JSON */
 	StringInfoData json_buf;	/* reusable buffer for JSON output */
+	JsonTypeCategory *json_categories;	/* per-column JSON type categories */
+	Oid		   *json_outfuncoids;	/* per-column JSON output func OIDs */
+	char	  **json_col_keys;	/* per-column pre-escaped "key": strings */

@@ -138,6 +140,8 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonStart(CopyToState cstate, TupleDesc tupDesc);
+static void CopyToJsonOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToJsonEnd(CopyToState cstate);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
@@ -160,8 +164,8 @@ static void CopySendInt16(CopyToState cstate, int16 val);
  * COPY TO routines for built-in formats.
  *
  * Text and CSV formats share the same TextLike routines except for the
- * one-row callback.  JSON shares the start and outfunc callbacks with
- * text/CSV, but has its own one-row and end callbacks.
+ * one-row callback.  JSON has its own start, outfunc, one-row, and end
+ * callbacks.
  */
 
 /* text format */
@@ -182,8 +186,8 @@ static const CopyToRoutine CopyToRoutineCSV = {
 
 /* json format */
 static const CopyToRoutine CopyToRoutineJson = {
-	.CopyToStart = CopyToTextLikeStart,
-	.CopyToOutFunc = CopyToTextLikeOutFunc,
+	.CopyToStart = CopyToJsonStart,
+	.CopyToOutFunc = CopyToJsonOutFunc,
 	.CopyToOneRow = CopyToJsonOneRow,
 	.CopyToEnd = CopyToJsonEnd,
 };
@@ -211,7 +215,7 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 	return &CopyToRoutineText;
 }
 
-/* Implementation of the start callback for text, CSV, and json formats */
+/* Implementation of the start callback for text and CSV formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -230,8 +234,6 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
-		Assert(cstate->opts.format != COPY_FORMAT_JSON);
-
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -251,30 +253,10 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 
 		CopySendTextLikeEndOfRow(cstate);
 	}
-
-	/* JSON-specific initialization */
-	if (cstate->opts.format == COPY_FORMAT_JSON)
-	{
-		MemoryContext oldcxt;
-
-		/* Allocate reusable JSON output buffer in long-lived context */
-		oldcxt = MemoryContextSwitchTo(cstate->copycontext);
-		initStringInfo(&cstate->json_buf);
-		MemoryContextSwitchTo(oldcxt);
-
-		/*
-		 * If FORCE_ARRAY has been specified, send the opening bracket.
-		 */
-		if (cstate->opts.force_array)
-		{
-			CopySendChar(cstate, '[');
-			CopySendTextLikeEndOfRow(cstate);
-		}
-	}
 }
 
 /*
- * Implementation of the outfunc callback for text, CSV, and json formats. Assign
+ * Implementation of the outfunc callback for text and CSV formats. Assign
  * the output function data to the given *finfo.
  */
 static void
@@ -354,34 +336,95 @@ CopyToTextLikeEnd(CopyToState cstate)
 	/* Nothing to do here */
 }
 
+/*
+ * Implementation of the start callback for json format.
+ *
+ * Pre-compute the escaped JSON key strings ('"colname":') for each selected
+ * column so CopyToJsonOneRow only needs to copy them per row.
+ */
+static void
+CopyToJsonStart(CopyToState cstate, TupleDesc tupDesc)
+{
+	MemoryContext oldcxt;
+	StringInfoData keybuf;
+
+	oldcxt = MemoryContextSwitchTo(cstate->copycontext);
+
+	/* Allocate reusable JSON output buffer */
+	initStringInfo(&cstate->json_buf);
+
+	/* Pre-build escaped key strings: "\"colname\":" */
+	cstate->json_col_keys = palloc0(tupDesc->natts * sizeof(char *));
+	initStringInfo(&keybuf);
+	foreach_int(attnum, cstate->attnumlist)
+	{
+		char	   *colname;
+
+		colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);
+
+		resetStringInfo(&keybuf);
+		escape_json(&keybuf, colname);
+		appendStringInfoChar(&keybuf, ':');
+
+		cstate->json_col_keys[attnum - 1] = pstrdup(keybuf.data);
+	}
+	pfree(keybuf.data);
+
+	MemoryContextSwitchTo(oldcxt);
+
+	/* If FORCE_ARRAY, send the opening bracket */
+	if (cstate->opts.force_array)
+	{
+		CopySendChar(cstate, '[');
+		CopySendTextLikeEndOfRow(cstate);
+	}
+}
+
+/*
+ * Implementation of the outfunc callback for json format.
+ *
+ * Instead of text output functions, we categorize each column's type for
+ * JSON serialization once so CopyToJsonOneRow can use datum_to_json_append
+ * directly.
+ */
+static void
+CopyToJsonOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo)
+{
+	int			attidx = finfo - cstate->out_functions;
+
+	json_categorize_type(atttypid, false,
+						 &cstate->json_categories[attidx],
+						 &cstate->json_outfuncoids[attidx]);
+}
+
 /* Implementation of per-row callback for json format */
 static void
 CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 {
-	Datum		rowdata;
+	bool		needsep = false;
 
-	/*
-	 * For query-based COPY, copy the query's TupleDesc attributes into the
-	 * slot's TupleDesc once.  BlessTupleDesc registers the RECORDOID
-	 * descriptor so that lookup_rowtype_tupdesc inside composite_to_json can
-	 * find it.
-	 */
-	if (!cstate->rel && !cstate->json_tupledesc_ready)
-	{
-		memcpy(TupleDescAttr(slot->tts_tupleDescriptor, 0),
-			   TupleDescAttr(cstate->queryDesc->tupDesc, 0),
-			   cstate->queryDesc->tupDesc->natts * sizeof(FormData_pg_attribute));
-
-		for (int i = 0; i < cstate->queryDesc->tupDesc->natts; i++)
-			populate_compact_attribute(slot->tts_tupleDescriptor, i);
-
-		BlessTupleDesc(slot->tts_tupleDescriptor);
-		cstate->json_tupledesc_ready = true;
-	}
-
-	rowdata = ExecFetchSlotHeapTupleDatum(slot);
 	resetStringInfo(&cstate->json_buf);
-	composite_to_json(rowdata, &cstate->json_buf, false);
+	appendStringInfoChar(&cstate->json_buf, '{');
+
+	foreach_int(attnum, cstate->attnumlist)
+	{
+		Datum		value = slot->tts_values[attnum - 1];
+		bool		isnull = slot->tts_isnull[attnum - 1];
+
+		if (needsep)
+			appendStringInfoChar(&cstate->json_buf, ',');
+		needsep = true;
+
+		/* Append pre-escaped "key": */
+		appendStringInfoString(&cstate->json_buf,
+							   cstate->json_col_keys[attnum - 1]);
+
+		datum_to_json_append(value, isnull, &cstate->json_buf,
+							 cstate->json_categories[attnum - 1],
+							 cstate->json_outfuncoids[attnum - 1]);
+	}
+
+	appendStringInfoChar(&cstate->json_buf, '}');
 
 	if (cstate->opts.force_array)
 	{
@@ -1004,12 +1047,6 @@ BeginCopyTo(ParseState *pstate,
 	/* Generate or convert list of attributes to process */
 	cstate->attnumlist = CopyGetAttnums(tupDesc, cstate->rel, attnamelist);
 
-	/* JSON outputs whole rows; a column list doesn't make sense */
-	if (cstate->opts.format == COPY_FORMAT_JSON && attnamelist != NIL)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("column selection is not supported in JSON mode")));
-
 	num_phys_attrs = tupDesc->natts;
 
 	/* Convert FORCE_QUOTE name list to per-column flags, check validity */
@@ -1204,6 +1241,12 @@ DoCopyTo(CopyToState cstate)
 
 	/* Get info about the columns we need to process. */
 	cstate->out_functions = (FmgrInfo *) palloc(num_phys_attrs * sizeof(FmgrInfo));
+	if (cstate->opts.format == COPY_FORMAT_JSON)
+	{
+		/* JSON outfunc callback stores per-column type categorization here */
+		cstate->json_categories = palloc0(num_phys_attrs * sizeof(JsonTypeCategory));
+		cstate->json_outfuncoids = palloc0(num_phys_attrs * sizeof(Oid));
+	}
 	foreach(cur, cstate->attnumlist)
 	{
 		int			attnum = lfirst_int(cur);
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index f609d7b9417..de81160a831 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -771,6 +771,20 @@ datum_to_json(Datum val, JsonTypeCategory tcategory, Oid outfuncoid)
 	return PointerGetDatum(cstring_to_text_with_len(result.data, result.len));
 }
 
+/*
+ * Append JSON representation of a Datum to a StringInfo.
+ *
+ * tcategory and outfuncoid are from a previous call to json_categorize_type.
+ * If is_null is true, appends "null" regardless of tcategory/outfuncoid.
+ */
+void
+datum_to_json_append(Datum val, bool is_null, StringInfo result,
+					 JsonTypeCategory tcategory, Oid outfuncoid)
+{
+	datum_to_json_internal(val, is_null, result, tcategory, outfuncoid,
+						   false);
+}
+
 /*
  * json_agg transition function
  *
diff --git a/src/include/utils/jsonfuncs.h b/src/include/utils/jsonfuncs.h
index 636f0f55840..12a01451fbb 100644
--- a/src/include/utils/jsonfuncs.h
+++ b/src/include/utils/jsonfuncs.h
@@ -85,6 +85,8 @@ extern void json_categorize_type(Oid typoid, bool is_jsonb,
 								 JsonTypeCategory *tcategory, Oid *outfuncoid);
 extern Datum datum_to_json(Datum val, JsonTypeCategory tcategory,
 						   Oid outfuncoid);
+extern void datum_to_json_append(Datum val, bool is_null, StringInfo result,
+								 JsonTypeCategory tcategory, Oid outfuncoid);
 extern Datum datum_to_jsonb(Datum val, JsonTypeCategory tcategory,
 							Oid outfuncoid);
 extern Datum jsonb_from_text(text *js, bool unique_keys);
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index a7e88b711d7..d60e5a4d32a 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -111,8 +111,6 @@ LINE 1: copy copytest to stdout (format json, on_error ignore);
                                               ^
 copy copytest from stdin(format json);
 ERROR:  COPY JSON mode cannot be used with COPY FROM
-copy copytest (style) to stdout (format json);
-ERROR:  column selection is not supported in JSON mode
 -- all of the above should yield error
 -- should fail: force_array requires json format
 copy copytest to stdout (format csv, force_array true);
@@ -137,6 +135,12 @@ copy copytest to stdout (format json, force_array false);
 {"style":"Unix","test":"abc\ndef","filler":2}
 {"style":"Mac","test":"abc\rdef","filler":3}
 {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- column list with json format
+copy copytest (style, filler) to stdout (format json);
+{"style":"DOS","filler":1}
+{"style":"Unix","filler":2}
+{"style":"Mac","filler":3}
+{"style":"esc\\ape","filler":4}
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index ae202fc5e8d..d64f4c66b93 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -99,7 +99,6 @@ copy copytest to stdout (format json, force_not_null *);
 copy copytest to stdout (format json, force_null *);
 copy copytest to stdout (format json, on_error ignore);
 copy copytest from stdin(format json);
-copy copytest (style) to stdout (format json);
 -- all of the above should yield error
 
 -- should fail: force_array requires json format
@@ -110,6 +109,9 @@ copy copytest to stdout (format json, force_array);
 copy copytest to stdout (format json, force_array true);
 copy copytest to stdout (format json, force_array false);
 
+-- column list with json format
+copy copytest (style, filler) to stdout (format json);
+
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
-- 
2.43.0

---

From: jian he <[email-masked]>
Date: Fri, 6 Mar 2026 17:38:30 +0800

COPY (SELECT 1 UNION ALL SELECT 2) TO stdout WITH (format json);

still fails with v25-0002, json_tupledesc_ready is not helpful.
I think I figured it out. We need to use BlessTupleDesc in BeginCopyTo.
Then let slot->tts_tupleDescriptor point to cstate->queryDesc->tupDesc
in CopyToJsonOneRow

 * CSV, text and json formats share the same TextLike routines except for the
 * one-row callback.
This comment is not useful, I want to delete it.

CopyToTextLikeStart
We ca just add

cstate->json_buf = makeStringInfo();

in BeginCopyTo.

v25-0004-COPY-TO-JSON-build-JSON-per-column-support-colum.patch
added several fields to the CopyToStateData.
Actually, there is a simpler way (construct a new Tupdesc and let
composite_to_json do the job), please see my v26-0004.

--
jian
https://www.enterprisedb.com/
From 61ea6a492ef900bf8745455847e2d9cffb396152 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Fri, 6 Mar 2026 14:47:58 +0800
Subject: [PATCH v26 3/4] Add option force_array for COPY JSON FORMAT

Author: Joe Conway <[email-masked]>
Author: jian he <[email-masked]>
Reviewed-by: Junwang Zhao <[email-masked]>
Reviewed-by: Masahiko Sawada <[email-masked]>,
Reviewed-by: Florents Tselai <[email-masked]>
Reviewed-by: Andrew Dunstan <[email-masked]>

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 30 ++++++++++++++++++++++
 src/backend/commands/copy.c        | 13 ++++++++++
 src/backend/commands/copyto.c      | 41 ++++++++++++++++++++++++++++--
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 33 ++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 10 ++++++++
 7 files changed, 127 insertions(+), 3 deletions(-)

 
+<para>

+	if (opts_out->format != COPY_FORMAT_JSON && opts_out->force_array)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s can only be used with JSON mode", "FORCE_ARRAY"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index e87310ec5a0..4ea44daee0a 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -86,6 +86,7 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+	bool		json_row_delim_needed;	/* need delimiter before next row */
 	StringInfo	json_buf;		/* reusable buffer for JSON output, it is
 								 * initliazed in BeginCopyTo  */
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
@@ -135,6 +136,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
 static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
+static void CopyToJsonEnd(CopyToState cstate);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -176,7 +178,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 	.CopyToStart = CopyToTextLikeStart,
 	.CopyToOutFunc = CopyToTextLikeOutFunc,
 	.CopyToOneRow = CopyToJsonOneRow,
-	.CopyToEnd = CopyToTextLikeEnd,
+	.CopyToEnd = CopyToJsonEnd,
 };
 
 /* binary format */
@@ -242,6 +244,18 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

 /*
@@ -318,13 +332,24 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }

+/* Implementation of the end callback for json format */
+static void
+CopyToJsonEnd(CopyToState cstate)
+{
+	if (cstate->opts.force_array)
+	{
+		CopySendChar(cstate, ']');
+		CopySendTextLikeEndOfRow(cstate);
+	}
+}
+
 /* Implementation of per-row callback for json format */
 static void
 CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
@@ -345,6 +370,18 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	rowdata = ExecFetchSlotHeapTupleDatum(slot);
 	composite_to_json(rowdata, cstate->json_buf, false);
 
 	CopySendData(cstate, cstate->json_buf->data, cstate->json_buf->len);
 
index 0d9649c1f0a..4b18cc6e2cd 100644
 
 /* COPY TO options */
 
 /*
  * These object types were introduced later than our support cutoff of
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 2b5bef6738e..abecfe51098 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -88,6 +88,7 @@ typedef struct CopyFormatOptions
 	List	   *force_notnull;	/* list of column names */
 	bool		force_notnull_all;	/* FORCE_NOT_NULL *? */
 	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+	bool		force_array;	/* add JSON array decorations */
 	List	   *force_null;		/* list of column names */
 	bool		force_null_all; /* FORCE_NULL *? */
 	bool	   *force_null_flags;	/* per-column CSV FN flags */
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 4324e3e4961..309a33ca2e7 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -80,6 +80,16 @@ copy (select 1 union all select 2) to stdout with (format json);
 copy (values (1), (2)) TO stdout with (format json);
 {"column1":1}
 {"column1":2}
+copy (select 1 union all select 2) to stdout with (format json, force_array true);
+[
+ {"?column?":1}
+,{"?column?":2}
+]
+copy (values (1), (2)) TO stdout with (format json, force_array true);
+[
+ {"column1":1}
+,{"column1":2}
+]
 copy copytest to stdout json;
 {"style":"DOS","test":"abc\r\ndef","filler":1}
 {"style":"Unix","test":"abc\ndef","filler":2}
@@ -122,6 +132,29 @@ ERROR:  COPY JSON mode cannot be used with COPY FROM
 copy copytest (style) to stdout (format json);
 ERROR:  column selection is not supported in JSON mode
 -- all of the above should yield error
+-- should fail: force_array requires json format
+copy copytest to stdout (format csv, force_array true);
+ERROR:  COPY FORCE_ARRAY can only be used with JSON mode
+-- force_array variants
+copy copytest to stdout (format json, force_array);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest to stdout (format json, force_array false);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 4e9f74537f8..8a20907dd4c 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -85,6 +85,8 @@ copy copytest3 to stdout csv header;
 --- test copying in JSON mode with various styles
 copy (select 1 union all select 2) to stdout with (format json);
 copy (values (1), (2)) TO stdout with (format json);
+copy (select 1 union all select 2) to stdout with (format json, force_array true);
+copy (values (1), (2)) TO stdout with (format json, force_array true);
 copy copytest to stdout json;
 copy copytest to stdout (format json);
 
@@ -105,6 +107,14 @@ copy copytest from stdin(format json);
 copy copytest (style) to stdout (format json);
 -- all of the above should yield error

From c531737641b7c0951b29b80144362168d1f96aa1 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Fri, 6 Mar 2026 17:30:23 +0800
Subject: [PATCH v26 4/4] COPY TO JSON support column lists

Author: Andrew Dunstan <[email-masked]>
Reviewed-by: jian he <[email-masked]>

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 src/backend/commands/copyto.c      | 54 +++++++++++++++++++++++++-----
 src/test/regress/expected/copy.out | 15 +++++++--
 src/test/regress/sql/copy.sql      |  5 ++-
 3 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 4ea44daee0a..a45ef6bcab3 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -89,6 +89,8 @@ typedef struct CopyToStateData
 	bool		json_row_delim_needed;	/* need delimiter before next row */
 	StringInfo	json_buf;		/* reusable buffer for JSON output, it is
 								 * initliazed in BeginCopyTo  */
+	TupleDesc	tupDesc;		/* Descriptor for the COPY TO column list.
+								 * This is only necessary for JSON output. */
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -359,11 +361,17 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	/*
 	 * composite_to_json() requires a stable TupleDesc. The slot's descriptor
 	 * (slot->tts_tupleDescriptor) may change during the execution of a SELECT
-	 * query, using cstate->queryDesc instead. No need worry this if COPY TO
-	 * is directly from a table.
+	 * query, using cstate->queryDesc instead.
+	 *
+	 * No need worry this if COPY TO is directly from a table, howeever when a
+	 * direct COPY TO from a table with a subset of columns in JSON mode, the
+	 * default slot's descriptor is obviously not OK, use the dedicated
+	 * TupleDesc constructed in BeginCopyTO.
 	 */
-	if (!cstate->rel)
-		slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
+	if (cstate->rel && (RelationGetDescr(cstate->rel) != cstate->tupDesc))
+		ReleaseTupleDesc(slot->tts_tupleDescriptor);
+
+	slot->tts_tupleDescriptor = cstate->tupDesc;
 
 	resetStringInfo(cstate->json_buf);
 
@@ -839,6 +847,7 @@ BeginCopyTo(ParseState *pstate,
 
 		tupDesc = RelationGetDescr(cstate->rel);
 		cstate->partitions = children;
+		cstate->tupDesc = tupDesc;
 	}
 	else
 	{
@@ -976,6 +985,7 @@ BeginCopyTo(ParseState *pstate,
 
 		tupDesc = cstate->queryDesc->tupDesc;
 		tupDesc = BlessTupleDesc(tupDesc);
+		cstate->tupDesc = tupDesc;
 	}
 
 	/* Generate or convert list of attributes to process */
@@ -986,10 +996,38 @@ BeginCopyTo(ParseState *pstate,
 	{
 		cstate->json_buf = makeStringInfo();
 
-		if (attnamelist != NIL)
-			ereport(ERROR,
-					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					errmsg("column selection is not supported in JSON mode"));
+		if (attnamelist != NIL && rel)
+		{
+			char	   *attname;
+			Oid			atttypid;
+			int32		atttypmod;
+			int			attdim;
+			TupleDesc	resultDesc;
+
+			/*
+			 * allocate a new tuple descriptor
+			 */
+			resultDesc = CreateTemplateTupleDesc(list_length(cstate->attnumlist));
+
+			foreach_int(attnum, cstate->attnumlist)
+			{
+				Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);
+
+				attname = NameStr(attr->attname);
+				atttypid = attr->atttypid;
+				atttypmod = attr->atttypmod;
+				attdim = attr->attndims;
+
+				TupleDescInitEntry(resultDesc,
+								   foreach_current_index(attnum) + 1,
+								   attname,
+								   atttypid,
+								   atttypmod,
+								   attdim);
+			}
+
+			cstate->tupDesc = BlessTupleDesc(resultDesc);
+		}
 	}
 
 	num_phys_attrs = tupDesc->natts;
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 309a33ca2e7..3ffb08bfada 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -129,8 +129,6 @@ copy copytest to stdout (format json, reject_limit 1);
 ERROR:  COPY REJECT_LIMIT requires ON_ERROR to be set to IGNORE
 copy copytest from stdin(format json);
 ERROR:  COPY JSON mode cannot be used with COPY FROM
-copy copytest (style) to stdout (format json);
-ERROR:  column selection is not supported in JSON mode
 -- all of the above should yield error
 -- should fail: force_array requires json format
 copy copytest to stdout (format csv, force_array true);
@@ -155,6 +153,19 @@ copy copytest to stdout (format json, force_array false);
 {"style":"Unix","test":"abc\ndef","filler":2}
 {"style":"Mac","test":"abc\rdef","filler":3}
 {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- column list with json format
+copy copytest (style, filler) to stdout (format json);
+{"style":"DOS","filler":1667391763}
+{"style":"Unix","filler":1701055075}
+{"style":"Mac","filler":1667391761}
+{"style":"esc\\ape","filler":1918656791}
+copy copytest (style, filler) to stdout (format json,  force_array true);
+[
+ {"style":"DOS","filler":1667391763}
+,{"style":"Unix","filler":1701055075}
+,{"style":"Mac","filler":1667391761}
+,{"style":"esc\\ape","filler":1918656791}
+]
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 8a20907dd4c..dae97bebb7d 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -104,7 +104,6 @@ copy copytest to stdout (format json, force_null *);
 copy copytest to stdout (format json, on_error ignore);
 copy copytest to stdout (format json, reject_limit 1);
 copy copytest from stdin(format json);
-copy copytest (style) to stdout (format json);
 -- all of the above should yield error
 
 -- should fail: force_array requires json format
@@ -115,6 +114,10 @@ copy copytest to stdout (format json, force_array);
 copy copytest to stdout (format json, force_array true);
 copy copytest to stdout (format json, force_array false);
 
+copy copytest (style, filler) to stdout (format json,  force_array true);

From 7244131f4710228f3e3998524dcd930e349e00bd Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Fri, 6 Mar 2026 14:32:48 +0800
Subject: [PATCH v26 2/4] json format for COPY TO

JSON format is incompatible with some standard text/CSV parsing or formatting options,
including:
- HEADER
- DEFAULT
- NULL
- DELIMITER
- FORCE QUOTE / FORCE NOT NULL

Author: jian he <[email-masked]>
Reviewed-by: Junwang Zhao <[email-masked]>

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 13 +++--
 src/backend/commands/copy.c        | 49 ++++++++++++-----
 src/backend/commands/copyto.c      | 85 +++++++++++++++++++++++++----
 src/backend/parser/gram.y          |  8 +++
 src/backend/utils/adt/json.c       |  5 +-
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/include/utils/json.h           |  2 +
 src/test/regress/expected/copy.out | 86 ++++++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 51 ++++++++++++++++++
 10 files changed, 271 insertions(+), 31 deletions(-)

 
      <note>

 
 
 	/* Check header */
 
 	/* Check quote */
 
index 0325a16f82a..e87310ec5a0 100644
@@ -84,6 +86,8 @@ typedef struct CopyToStateData
+	StringInfo	json_buf;		/* reusable buffer for JSON output, it is
+								 * initliazed in BeginCopyTo  */
 
 	CopyFormatOptions opts;
@@ -130,6 +134,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -148,9 +153,6 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 
 /*
- *
 
 /* text format */
@@ -169,6 +171,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
@@ -185,12 +195,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 
 	/* default is text */
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -209,6 +221,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -231,7 +245,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 }
 
 /*
@@ -304,13 +318,38 @@ CopyToTextLikeOneRow(CopyToState cstate,

+/* Implementation of per-row callback for json format */
+static void
+CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
+{
+	Datum		rowdata;
+
+	/*
+	 * composite_to_json() requires a stable TupleDesc. The slot's descriptor
+	 * (slot->tts_tupleDescriptor) may change during the execution of a SELECT
+	 * query, using cstate->queryDesc instead. No need worry this if COPY TO
+	 * is directly from a table.
+	 */
+	if (!cstate->rel)
+		slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
+
+	resetStringInfo(cstate->json_buf);
+
+	rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	composite_to_json(rowdata, cstate->json_buf, false);
+
+	CopySendData(cstate, cstate->json_buf->data, cstate->json_buf->len);
+
+	CopySendTextLikeEndOfRow(cstate);
+}
+
 /*
  * Implementation of the start callback for binary format. Send a header
  * for a binary copy.
@@ -402,9 +441,23 @@ SendCopyBegin(CopyToState cstate)
 
@@ -506,7 +559,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
- * Wrapper function of CopySendEndOfRow for text and CSV formats. Sends the
+ * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the
  * line termination and do common appropriate things for the end of row.
  */
 static inline void
@@ -885,11 +938,23 @@ BeginCopyTo(ParseState *pstate,
 		ExecutorStart(cstate->queryDesc, 0);
 
 		tupDesc = cstate->queryDesc->tupDesc;
+		tupDesc = BlessTupleDesc(tupDesc);
 	}

+	/* JSON outputs whole rows; a column list doesn't make sense */
+	if (cstate->opts.format == COPY_FORMAT_JSON)
+	{
+		cstate->json_buf = makeStringInfo();
+
+		if (attnamelist != NIL)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("column selection is not supported in JSON mode"));
+	}
+
 	num_phys_attrs = tupDesc->natts;
 
 	/* Convert FORCE_QUOTE name list to per-column flags, check validity */
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 3c3e24324a8..40ad9073901 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3612,6 +3612,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("format", (Node *) makeString("csv"), @1);
 				}
+			| JSON
+				{
+					$$ = makeDefElem("format", (Node *) makeString("json"), @1);
+				}
 			| HEADER_P
 				{
 					$$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3694,6 +3698,10 @@ copy_generic_opt_elem:
 				{
 					$$ = makeDefElem($1, $2, @1);
 				}
+			| FORMAT_LA copy_generic_opt_arg
+				{
+					$$ = makeDefElem("format", $2, @1);
+				}
 		;
 
 copy_generic_opt_arg:

 /*
index f8c0865ca89..0d9649c1f0a 100644

 
 /*
 
index d0d563e0fa8..4324e3e4961 100644
@@ -73,6 +73,92 @@ copy copytest3 to stdout csv header;
+copy (select 1 union all select 2) to stdout with (format json);
+{"?column?":1}
+{"?column?":2}
+copy (values (1), (2)) TO stdout with (format json);
+{"column1":1}
+{"column1":2}
+copy copytest to stdout (format json, reject_limit 1);
+ERROR:  COPY REJECT_LIMIT requires ON_ERROR to be set to IGNORE
index 65cbdaf7f3e..4e9f74537f8 100644
@@ -82,6 +82,57 @@ this is just a line full of junk that would error out if parsed

+copy (select 1 union all select 2) to stdout with (format json);
+copy (values (1), (2)) TO stdout with (format json);
+copy copytest to stdout (format json, reject_limit 1);

From e4747ff8a87e79edb8fd3b7778bcbe8a3a6e85f7 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:38:24 +0800
Subject: [PATCH v26 1/4] introduce CopyFormat refactor CopyFormatOptions

 

 

 
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

 
 	/* default is text */

 /*

 
 	/* default is text */

 
 
+/*

---

From: jian he <[email-masked]>
Date: Mon, 9 Mar 2026 00:16:08 +0800

hi.

V27-0002 is still not bullet-proof.

drop table if exists t1;
create table t1(a int);
insert into t1 values (1);
copy (select * from t1) to stdout json;
{"a":1}
WARNING:  resource was not closed: TupleDesc 0x7171d0ca3440 (18239,-1)

Also see ExecAssignScanProjectionInfo->ExecConditionalAssignProjectionInfo
So in v28-0002, I changed to
+    /*
+     * composite_to_json() requires a stable TupleDesc. Since the slot's
+     * descriptor (slot->tts_tupleDescriptor) can change during the execution
+     * of a SELECT query, we use cstate->queryDesc->tupDesc instead. This
+     * precaution is only necessary when the output slot's TupleDesc is of
+     * type RECORDOID.
+     */
+    if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == RECORDOID)
+        slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;

+ cstate->json_projvalues = (Datum *) palloc(natts * sizeof(Datum));
+ cstate->json_projnulls = (bool *) palloc(natts * sizeof(bool));
I changed it to
+            cstate->json_projvalues = palloc_array(Datum, natts);
+            cstate->json_projnulls = palloc_array(bool, natts);

+ rowdata = HeapTupleHeaderGetDatum(tup->t_data);
I changed it to
+        rowdata = HeapTupleGetDatum(tup);

Patch v28-0004 adds the json_projvalues and json_projnulls pointers to struct
CopyToStateData. I wondered if adding these would slow the COPY TO with TEXT and
CSV format, so I ran a quick test using a 36-column table.

Surprisingly, v28 actually make COPY TO with TEXT and CSV performs a little bit
faster. But I didn't find out why.
You may also try the attached test script: copyto_json_perfomance_test.nocfbot.

--
jian
https://www.enterprisedb.com/
From 439fc107c50408f51e3192f221373e1333672063 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sun, 8 Mar 2026 23:44:11 +0800
Subject: [PATCH v28 2/4] json format for COPY TO

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 13 +++--
 src/backend/commands/copy.c        | 49 +++++++++++-----
 src/backend/commands/copyto.c      | 86 ++++++++++++++++++++++++----
 src/backend/parser/gram.y          |  8 +++
 src/backend/utils/adt/json.c       |  5 +-
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/include/utils/json.h           |  2 +
 src/test/regress/expected/copy.out | 91 ++++++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 52 +++++++++++++++++
 10 files changed, 278 insertions(+), 31 deletions(-)

 
      <note>

 
 
 	/* Check header */
 
 	/* Check quote */
 
index b0ee91fc9c1..6971f4b85af 100644
@@ -85,6 +87,8 @@ typedef struct CopyToStateData
 
 	CopyFormatOptions opts;
@@ -131,6 +135,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -149,9 +154,6 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 
 /*
 
 /* text format */
@@ -170,6 +172,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
@@ -186,12 +196,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 
 	/* default is text */
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -210,6 +222,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -232,7 +246,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 }
 
 /*
@@ -305,13 +319,39 @@ CopyToTextLikeOneRow(CopyToState cstate,

+/* Implementation of per-row callback for json format */
+static void
+CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
+{
+	Datum		rowdata;
+
+	/*
+	 * composite_to_json() requires a stable TupleDesc. Since the slot's
+	 * descriptor (slot->tts_tupleDescriptor) can change during the execution
+	 * of a SELECT query, we use cstate->queryDesc->tupDesc instead. This
+	 * precaution is only necessary when the output slot's TupleDesc is of
+	 * type RECORDOID.
+	 */
+	if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == RECORDOID)
+		slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
+
+	resetStringInfo(cstate->json_buf);
+
+	rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	composite_to_json(rowdata, cstate->json_buf, false);
+
+	CopySendData(cstate, cstate->json_buf->data, cstate->json_buf->len);
+
+	CopySendTextLikeEndOfRow(cstate);
+}
+
 /*
  * Implementation of the start callback for binary format. Send a header
  * for a binary copy.
@@ -403,9 +443,23 @@ SendCopyBegin(CopyToState cstate)
 
@@ -507,7 +561,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
@@ -886,11 +940,23 @@ BeginCopyTo(ParseState *pstate,

 
 
index 9cbe8eafc45..136fd19b854 100644
 
 copy_generic_opt_arg:

 /*
index 6484c6a3dd4..bb82bdbcc48 100644

 
 /*
 
index d0d563e0fa8..72011f3492c 100644
@@ -73,6 +73,97 @@ copy copytest3 to stdout csv header;
+copy (select * from copytest) to stdout (format json);
index 65cbdaf7f3e..a6c923ef5ab 100644
@@ -82,6 +82,58 @@ this is just a line full of junk that would error out if parsed

+copy (select * from copytest) to stdout (format json);

From 226c834e93351ffda039774fbd4b57a9ab16b4f7 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:38:24 +0800
Subject: [PATCH v28 1/4] introduce CopyFormat refactor CopyFormatOptions

 

 

 
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

 
 	/* default is text */
index 84c8809a889..5f0c551e7ec 100644
@@ -173,7 +173,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 
@@ -751,7 +751,7 @@ bool
 
 /*
@@ -778,7 +778,8 @@ NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields
 	bool		done = false;

index d6ef7275a64..b0ee91fc9c1 100644
@@ -182,9 +182,9 @@ static const CopyToRoutine CopyToRoutineBinary = {
 
 	/* default is text */
@@ -221,7 +221,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

@@ -398,7 +398,7 @@ SendCopyBegin(CopyToState cstate)

+/*
index 3250564d4ff..520cdd36800 100644

From 247eceeeaec62677d899f225bd83905da21f0087 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sun, 8 Mar 2026 15:54:23 +0800
Subject: [PATCH v28 3/4] Add option force_array for COPY JSON FORMAT

 
 
+<para>

index 6971f4b85af..38fbf7d4424 100644
@@ -87,6 +87,7 @@ typedef struct CopyToStateData
@@ -136,6 +137,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
@@ -177,7 +179,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 
 /* binary format */
@@ -243,6 +245,18 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

 /*
@@ -319,13 +333,24 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }

@@ -347,6 +372,18 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)

index bb82bdbcc48..00458cfb4bc 100644
 
 /* COPY TO options */
 
 /*
index 72011f3492c..e1d51335e33 100644
@@ -127,6 +137,29 @@ ERROR:  COPY JSON mode cannot be used with COPY FROM
index a6c923ef5ab..764d19f4947 100644
 copy (select * from copytest) to stdout (format json);
@@ -106,6 +108,14 @@ copy copytest from stdin(format json);

From 365f340a0b733a3d9b5fdf540a2623c3ea9d4d8d Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Sun, 8 Mar 2026 23:58:29 +0800
Subject: [PATCH v28 4/4] COPY TO JSON: support column lists

When a column list is specified (e.g. COPY t (a, b) TO ... FORMAT json),
build a projected TupleDesc containing only the selected columns and
form a new tuple per row via heap_form_tuple(), so that composite_to_json()
emits the correct column names and values.

Use HeapTupleHeaderGetDatum() directly on the formed tuple rather than
heap_copy_tuple_as_datum(), since heap_form_tuple() already stamps the
datum-length, type-id, and type-mod fields on t_data, avoiding an
unnecessary palloc+memcpy per row.

Add regression tests covering column lists with diverse data types
including json, jsonb, int[], numeric, boolean, timestamp, and text,
exercising various column subsets and NULL handling.

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 src/backend/commands/copyto.c      | 105 ++++++++++++++++++++++++-----
 src/test/regress/expected/copy.out |  73 +++++++++++++++++++-
 src/test/regress/sql/copy.sql      |  40 ++++++++++-
 3 files changed, 197 insertions(+), 21 deletions(-)

diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 38fbf7d4424..faa8e323f56 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -88,8 +88,13 @@ typedef struct CopyToStateData
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
 	bool		json_row_delim_needed;	/* need delimiter before next row */
-	StringInfo	json_buf;		/* reusable buffer for JSON output, it is
-								 * initliazed in BeginCopyTo  */
+	StringInfo	json_buf;		/* reusable buffer for JSON output,
+								 * initialized in BeginCopyTo */
+	TupleDesc	tupDesc;		/* Descriptor for JSON output; for a column
+								 * list this is a projected descriptor */
+	Datum	   *json_projvalues;	/* pre-allocated projection values, or
+									 * NULL */
+	bool	   *json_projnulls; /* pre-allocated projection nulls, or NULL */
 	copy_data_dest_cb data_dest_cb; /* function for writing data */
 
 	CopyFormatOptions opts;
@@ -357,19 +362,53 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 {
 	Datum		rowdata;
 
-	/*
-	 * composite_to_json() requires a stable TupleDesc. Since the slot's
-	 * descriptor (slot->tts_tupleDescriptor) can change during the execution
-	 * of a SELECT query, we use cstate->queryDesc->tupDesc instead. This
-	 * precaution is only necessary when the output slot's TupleDesc is of
-	 * type RECORDOID.
-	 */
-	if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == RECORDOID)
-		slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
-
 	resetStringInfo(cstate->json_buf);
 
-	rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	if (cstate->json_projvalues != NULL)
+	{
+		/*
+		 * Column list case: project selected column values into sequential
+		 * positions matching the custom TupleDesc, then form a new tuple.
+		 */
+		HeapTuple	tup;
+		int			i = 0;
+
+		foreach_int(attnum, cstate->attnumlist)
+		{
+			cstate->json_projvalues[i] = slot->tts_values[attnum - 1];
+			cstate->json_projnulls[i] = slot->tts_isnull[attnum - 1];
+			i++;
+		}
+
+		tup = heap_form_tuple(cstate->tupDesc,
+							  cstate->json_projvalues,
+							  cstate->json_projnulls);
+
+		/*
+		 * heap_form_tuple already stamps the datum-length, type-id, and
+		 * type-mod fields on t_data, so we can use it directly as a composite
+		 * Datum without the extra pallocmemcpy that heap_copy_tuple_as_datum
+		 * would do.  Any TOAST pointers in the projected values will be
+		 * detoasted by the per-column output functions called from
+		 * composite_to_json.
+		 */
+		rowdata = HeapTupleGetDatum(tup);
+	}
+	else
+	{
+		/*
+		 * Full table or query without column list.  Ensure the slot uses
+		 * cstate->tupDesc so that the datum is stamped with the right type;
+		 * for queries output type is RECORDOID this must be the blessed
+		 * descriptor so that composite_to_json can look it up via
+		 * lookup_rowtype_tupdesc.
+		 */
+		if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == RECORDOID)
+			slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
+
+		rowdata = ExecFetchSlotHeapTupleDatum(slot);
+	}
+
 	composite_to_json(rowdata, cstate->json_buf, false);
 
 	if (cstate->opts.force_array)
@@ -841,6 +880,7 @@ BeginCopyTo(ParseState *pstate,
 
 		tupDesc = RelationGetDescr(cstate->rel);
 		cstate->partitions = children;
+		cstate->tupDesc = tupDesc;
 	}
 	else
 	{
@@ -978,20 +1018,49 @@ BeginCopyTo(ParseState *pstate,

 
-	/* JSON outputs whole rows; a column list doesn't make sense */
+	/* Set up JSON-specific state */
 	if (cstate->opts.format == COPY_FORMAT_JSON)
 	{
 		cstate->json_buf = makeStringInfo();
 
-		if (attnamelist != NIL)
-			ereport(ERROR,
-					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					errmsg("column selection is not supported in JSON mode"));
+		if (attnamelist != NIL && rel)
+		{
+			int			natts = list_length(cstate->attnumlist);
+			TupleDesc	resultDesc;
+
+			/*
+			 * Build a TupleDesc describing only the selected columns so that
+			 * composite_to_json() emits the right column names and types.
+			 */
+			resultDesc = CreateTemplateTupleDesc(natts);
+
+			foreach_int(attnum, cstate->attnumlist)
+			{
+				Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);
+
+				TupleDescInitEntry(resultDesc,
+								   foreach_current_index(attnum) + 1,
+								   NameStr(attr->attname),
+								   attr->atttypid,
+								   attr->atttypmod,
+								   attr->attndims);
+			}
+
+			cstate->tupDesc = BlessTupleDesc(resultDesc);
+
+			/*
+			 * Pre-allocate arrays for projecting selected column values into
+			 * sequential positions matching the custom TupleDesc.
+			 */
+			cstate->json_projvalues = palloc_array(Datum, natts);
+			cstate->json_projnulls = palloc_array(bool, natts);
+		}
 	}
 
 	num_phys_attrs = tupDesc->natts;
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index e1d51335e33..e44b4a1d79d 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -77,6 +77,9 @@ c1,"col with , comma","col with "" quote"
 copy (select 1 union all select 2) to stdout with (format json);
 {"?column?":1}
 {"?column?":2}
+copy (select 1 as foo union all select 2) to stdout with (format json);
+{"foo":1}
+{"foo":2}
 copy (values (1), (2)) TO stdout with (format json);
 {"column1":1}
 {"column1":2}
@@ -134,8 +137,6 @@ copy copytest to stdout (format json, reject_limit 1);
 ERROR:  COPY REJECT_LIMIT requires ON_ERROR to be set to IGNORE
 copy copytest from stdin(format json);
 ERROR:  COPY JSON mode cannot be used with COPY FROM
-copy copytest (style) to stdout (format json);
-ERROR:  column selection is not supported in JSON mode
 -- all of the above should yield error
 -- should fail: force_array requires json format
 copy copytest to stdout (format csv, force_array true);
@@ -160,6 +161,74 @@ copy copytest to stdout (format json, force_array false);
 {"style":"Unix","test":"abc\ndef","filler":2}
 {"style":"Mac","test":"abc\rdef","filler":3}
 {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- column list with json format
+copy copytest (style, filler) to stdout (format json);
+{"style":"DOS","filler":1}
+{"style":"Unix","filler":2}
+{"style":"Mac","filler":3}
+{"style":"esc\\ape","filler":4}
+copy copytest (style, filler) to stdout (format json,  force_array true);
+[
+ {"style":"DOS","filler":1}
+,{"style":"Unix","filler":2}
+,{"style":"Mac","filler":3}
+,{"style":"esc\\ape","filler":4}
+]
+copy copytest (style, test, filler) to stdout (format json,  force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+-- column list with diverse data types
+create temp table copyjsontest_types (
+    id int,
+    js json,
+    jsb jsonb,
+    arr int[],
+    n numeric(10,2),
+    b boolean,
+    ts timestamp,
+    t text);
+insert into copyjsontest_types values
+(1, '{"a":1}', '{"b":2}', '{1,2,3}', 3.14, true,
+ '2024-01-15 10:30:00', 'hello'),
+(2, '[1,null,"x"]', '{"nested":{"k":"v"}}', '{4,5}', -99.99, false,
+ '2024-06-30 23:59:59', 'world'),
+(3, 'null', 'null', '{}', null, null, null, null);
+-- full table
+copy copyjsontest_types to stdout (format json);
+{"id":1,"js":{"a":1},"jsb":{"b": 2},"arr":[1,2,3],"n":3.14,"b":true,"ts":"2024-01-15T10:30:00","t":"hello"}
+{"id":2,"js":[1,null,"x"],"jsb":{"nested": {"k": "v"}},"arr":[4,5],"n":-99.99,"b":false,"ts":"2024-06-30T23:59:59","t":"world"}
+{"id":3,"js":null,"jsb":null,"arr":[],"n":null,"b":null,"ts":null,"t":null}
+-- column subsets exercising each type
+copy copyjsontest_types (id, js, jsb) to stdout (format json);
+{"id":1,"js":{"a":1},"jsb":{"b": 2}}
+{"id":2,"js":[1,null,"x"],"jsb":{"nested": {"k": "v"}}}
+{"id":3,"js":null,"jsb":null}
+copy copyjsontest_types (id, arr, n, b) to stdout (format json);
+{"id":1,"arr":[1,2,3],"n":3.14,"b":true}
+{"id":2,"arr":[4,5],"n":-99.99,"b":false}
+{"id":3,"arr":[],"n":null,"b":null}
+copy copyjsontest_types (jsb, t) to stdout (format json);
+{"jsb":{"b": 2},"t":"hello"}
+{"jsb":{"nested": {"k": "v"}},"t":"world"}
+{"jsb":null,"t":null}
+copy copyjsontest_types (id, ts) to stdout (format json);
+{"id":1,"ts":"2024-01-15T10:30:00"}
+{"id":2,"ts":"2024-06-30T23:59:59"}
+{"id":3,"ts":null}
+-- single column: json and jsonb
+copy copyjsontest_types (js) to stdout (format json);
+{"js":{"a":1}}
+{"js":[1,null,"x"]}
+{"js":null}
+copy copyjsontest_types (jsb) to stdout (format json);
+{"jsb":{"b": 2}}
+{"jsb":{"nested": {"k": "v"}}}
+{"jsb":null}
+drop table copyjsontest_types;
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 764d19f4947..e4e70a82ecc 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -84,6 +84,7 @@ copy copytest3 to stdout csv header;
 
 --- test copying in JSON mode with various styles
 copy (select 1 union all select 2) to stdout with (format json);
+copy (select 1 as foo union all select 2) to stdout with (format json);
 copy (values (1), (2)) TO stdout with (format json);
 copy (select 1 union all select 2) to stdout with (format json, force_array true);
 copy (values (1), (2)) TO stdout with (format json, force_array true);
@@ -105,7 +106,6 @@ copy copytest to stdout (format json, force_null *);
 copy copytest to stdout (format json, on_error ignore);
 copy copytest to stdout (format json, reject_limit 1);
 copy copytest from stdin(format json);
-copy copytest (style) to stdout (format json);
 -- all of the above should yield error
 
 -- should fail: force_array requires json format
@@ -116,6 +116,44 @@ copy copytest to stdout (format json, force_array);
 copy copytest to stdout (format json, force_array true);
 copy copytest to stdout (format json, force_array false);
 
+-- column list with json format
+copy copytest (style, filler) to stdout (format json);
+copy copytest (style, filler) to stdout (format json,  force_array true);
+copy copytest (style, test, filler) to stdout (format json,  force_array true);
+
+-- column list with diverse data types
+create temp table copyjsontest_types (
+    id int,
+    js json,
+    jsb jsonb,
+    arr int[],
+    n numeric(10,2),
+    b boolean,
+    ts timestamp,
+    t text);
+
+insert into copyjsontest_types values
+(1, '{"a":1}', '{"b":2}', '{1,2,3}', 3.14, true,
+ '2024-01-15 10:30:00', 'hello'),
+(2, '[1,null,"x"]', '{"nested":{"k":"v"}}', '{4,5}', -99.99, false,
+ '2024-06-30 23:59:59', 'world'),
+(3, 'null', 'null', '{}', null, null, null, null);
+
+-- full table
+copy copyjsontest_types to stdout (format json);
+
+-- column subsets exercising each type
+copy copyjsontest_types (id, js, jsb) to stdout (format json);
+copy copyjsontest_types (id, arr, n, b) to stdout (format json);
+copy copyjsontest_types (jsb, t) to stdout (format json);
+copy copyjsontest_types (id, ts) to stdout (format json);
+
+-- single column: json and jsonb
+copy copyjsontest_types (js) to stdout (format json);
+copy copyjsontest_types (jsb) to stdout (format json);
+
+drop table copyjsontest_types;
+
 -- embedded escaped characters
 create temp table copyjsontest (
     id bigserial,
-- 
2.34.1

---

From: Andrew Dunstan <[email-masked]>
Date: Sun, 8 Mar 2026 15:44:51 -0400

> +        slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;

Hmm. But should we be scribbling on slot->tts_tupleDescriptor like that? 
How about something like this?:

-        * Full table or query without column list.  Ensure the slot uses
-        * cstate->tupDesc so that the datum is stamped with the right type;
-        * for queries output type is RECORDOID this must be the blessed
-        * descriptor so that composite_to_json can look it up via
-        * lookup_rowtype_tupdesc.
+        * Full table or query without column list.  For queries, the slot's
+        * TupleDesc may carry RECORDOID, which is not registered in the 
type
+        * cache and would cause composite_to_json's lookup_rowtype_tupdesc
+        * call to fail.  Build a HeapTuple stamped with the blessed
+        * descriptor so the type can be looked up correctly.
          */
         if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == 
RECORDOID)
-           slot->tts_tupleDescriptor = cstate->queryDesc->tupDesc;
+       {
+           HeapTuple   tup;

+                                 slot->tts_values,
+                                 slot->tts_isnull);

cheers

andrew

---

From: jian he <[email-masked]>
Date: Mon, 9 Mar 2026 11:48:26 +0800

> +           rowdata = ExecFetchSlotHeapTupleDatum(slot);
This is better. I've tried to get rid of json_projvalues and json_projnulls.
Just using heap_form_tuple, but it won't work.

I incorporated the v28-0004 COPY column list into v9-0002.
With this patch set, we added four fields to the struct CopyToStateData.

Using the script in
https://www.postgresql.org/message-id/CACJufxFFZqxC3p4WjpTEi4riaJm%3DpADX%2Bpy0yQ0%3DRWTn5cqK3Q%40mail.gmail.com
I tested it again on macOS and Linux, and there are no regressions for
COPY TO with the TEXT and CSV formats.

--
jian
https://www.enterprisedb.com/
From e9fdfae2f0829b2af2e5ee4047230ec124bd72b9 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 9 Mar 2026 10:21:32 +0800
Subject: [PATCH v29 2/3] json format for COPY TO

Author: Andrew Dunstan <[email-masked]>,

discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         |  13 ++-
 src/backend/commands/copy.c        |  49 ++++++---
 src/backend/commands/copyto.c      | 161 +++++++++++++++++++++++++++--
 src/backend/parser/gram.y          |   8 ++
 src/backend/utils/adt/json.c       |   5 +-
 src/bin/psql/tab-complete.in.c     |   2 +-
 src/include/commands/copy.h        |   1 +
 src/include/utils/json.h           |   2 +
 src/test/regress/expected/copy.out | 146 ++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      |  88 ++++++++++++++++
 10 files changed, 444 insertions(+), 31 deletions(-)

 
      <note>

 
 
 	/* Check header */
 
 	/* Check quote */
 
index b0ee91fc9c1..9d8d8318957 100644
@@ -85,6 +87,13 @@ typedef struct CopyToStateData
 
 	CopyFormatOptions opts;
@@ -131,6 +140,7 @@ static void CopyToCSVOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
+static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -149,9 +159,6 @@ static void CopySendInt16(CopyToState cstate, int16 val);
 
 /*
 
 /* text format */
@@ -170,6 +177,14 @@ static const CopyToRoutine CopyToRoutineCSV = {
 	.CopyToEnd = CopyToTextLikeEnd,
 };
 
+/* json format */
@@ -186,12 +201,14 @@ CopyToGetRoutine(const CopyFormatOptions *opts)
 
 	/* default is text */
 
-/* Implementation of the start callback for text and CSV formats */
+/* Implementation of the start callback for text, CSV, and json formats */
 static void
 CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 {
@@ -210,6 +227,8 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 		ListCell   *cur;
 		bool		hdr_delim = false;
 
+		Assert(cstate->opts.format != COPY_FORMAT_JSON);
+
 		foreach(cur, cstate->attnumlist)
 		{
 			int			attnum = lfirst_int(cur);
@@ -232,7 +251,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 }
 
 /*
@@ -305,13 +324,79 @@ CopyToTextLikeOneRow(CopyToState cstate,

+		 * TupleDesc may carry RECORDOID, which is not registered in the type
+			HeapTuple	tup = heap_form_tuple(cstate->tupDesc,
@@ -403,9 +488,23 @@ SendCopyBegin(CopyToState cstate)
 
@@ -507,7 +606,7 @@ CopySendEndOfRow(CopyToState cstate)
 }
 
 /*
- * Wrapper function of CopySendEndOfRow for text and CSV formats. Sends the
+ * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the
  * line termination and do common appropriate things for the end of row.
  */
 static inline void
@@ -750,6 +849,7 @@ BeginCopyTo(ParseState *pstate,
 
@@ -886,11 +986,52 @@ BeginCopyTo(ParseState *pstate,

 
+			 * * Pre-allocate arrays for projecting selected column values
+			 * into  sequential positions matching the custom TupleDesc.

 copy_generic_opt_arg:

 /*

 
 /*
 
index d0d563e0fa8..9b667544905 100644
@@ -73,6 +73,152 @@ copy copytest3 to stdout csv header;
+copy copytest (style, test, filler) to stdout (format json);
index 65cbdaf7f3e..404f4321085 100644
@@ -82,6 +82,94 @@ this is just a line full of junk that would error out if parsed

+copy copytest (style, test, filler) to stdout (format json);

From cc747df3929913078b85dd5fbee5a852aa7d0d53 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Wed, 21 Jan 2026 18:38:24 +0800
Subject: [PATCH v29 1/3] introduce CopyFormat refactor CopyFormatOptions

 

 

 
 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

 
 	/* default is text */

 /*

 
 	/* default is text */

 
 
+/*

From 510f1f0435bc74b80575b0b8af2134817fedfa05 Mon Sep 17 00:00:00 2001
From: jian he <[email-masked]>
Date: Mon, 9 Mar 2026 10:27:37 +0800
Subject: [PATCH v29 3/3] Add option force_array for COPY JSON FORMAT

 
 
+<para>

+	if (opts_out->format != COPY_FORMAT_JSON && opts_out->force_array)
+		ereport(ERROR,
+				errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("COPY %s can only be used with JSON mode", "FORCE_ARRAY"));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 9d8d8318957..85ca7c947f3 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -87,6 +87,7 @@ typedef struct CopyToStateData
 	List	   *attnumlist;		/* integer list of attnums to copy */
 	char	   *filename;		/* filename, or NULL for STDOUT */
 	bool		is_program;		/* is 'filename' a program to popen? */
+	bool		json_row_delim_needed;	/* need delimiter before next row */
 	StringInfo	json_buf;		/* reusable buffer for JSON output,
 								 * initialized in BeginCopyTo */
 	TupleDesc	tupDesc;		/* Descriptor for JSON output; for a column
@@ -141,6 +142,7 @@ static void CopyToTextLikeOneRow(CopyToState cstate, TupleTableSlot *slot,
 								 bool is_csv);
 static void CopyToTextLikeEnd(CopyToState cstate);
 static void CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot);
+static void CopyToJsonEnd(CopyToState cstate);
 static void CopyToBinaryStart(CopyToState cstate, TupleDesc tupDesc);
 static void CopyToBinaryOutFunc(CopyToState cstate, Oid atttypid, FmgrInfo *finfo);
 static void CopyToBinaryOneRow(CopyToState cstate, TupleTableSlot *slot);
@@ -182,7 +184,7 @@ static const CopyToRoutine CopyToRoutineJson = {
 	.CopyToStart = CopyToTextLikeStart,
 	.CopyToOutFunc = CopyToTextLikeOutFunc,
 	.CopyToOneRow = CopyToJsonOneRow,
-	.CopyToEnd = CopyToTextLikeEnd,
+	.CopyToEnd = CopyToJsonEnd,
 };
 
 /* binary format */
@@ -248,6 +250,18 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

 /*
@@ -324,13 +338,24 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }

@@ -392,6 +417,18 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)

 
 
 /* COPY TO options */
 
 /*
  * These object types were introduced later than our support cutoff of
diff --git a/src/include/commands/copy.h b/src/include/commands/copy.h
index 2b5bef6738e..abecfe51098 100644
--- a/src/include/commands/copy.h
+++ b/src/include/commands/copy.h
@@ -88,6 +88,7 @@ typedef struct CopyFormatOptions
 	List	   *force_notnull;	/* list of column names */
 	bool		force_notnull_all;	/* FORCE_NOT_NULL *? */
 	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+	bool		force_array;	/* add JSON array decorations */
 	List	   *force_null;		/* list of column names */
 	bool		force_null_all; /* FORCE_NULL *? */
 	bool	   *force_null_flags;	/* per-column CSV FN flags */
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 9b667544905..bcf45845b61 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -83,6 +83,16 @@ copy (select 1 as foo union all select 2) to stdout with (format json);
 copy (values (1), (2)) TO stdout with (format json);
 {"column1":1}
 {"column1":2}
+copy (select 1 union all select 2) to stdout with (format json, force_array true);
+[
+ {"?column?":1}
+,{"?column?":2}
+]
+copy (values (1), (2)) TO stdout with (format json, force_array true);
+[
+ {"column1":1}
+,{"column1":2}
+]
 copy copytest to stdout json;
 {"style":"DOS","test":"abc\r\ndef","filler":1}
 {"style":"Unix","test":"abc\ndef","filler":2}
@@ -134,6 +144,29 @@ copy copytest (style, test, filler) to stdout (format json);
 {"style":"Unix","test":"abc\ndef","filler":2}
 {"style":"Mac","test":"abc\rdef","filler":3}
 {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- should fail: force_array requires json format
+copy copytest to stdout (format csv, force_array true);
+ERROR:  COPY FORCE_ARRAY can only be used with JSON mode
+-- force_array variants
+copy copytest to stdout (format json, force_array);
+[
+ {"style":"DOS","test":"abc\r\ndef","filler":1}
+,{"style":"Unix","test":"abc\ndef","filler":2}
+,{"style":"Mac","test":"abc\rdef","filler":3}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+]
+copy copytest(style, test) to stdout (format json, force_array true);
+[
+ {"style":"DOS","test":"abc\r\ndef"}
+,{"style":"Unix","test":"abc\ndef"}
+,{"style":"Mac","test":"abc\rdef"}
+,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb"}
+]
+copy copytest to stdout (format json, force_array false);
+{"style":"DOS","test":"abc\r\ndef","filler":1}
+{"style":"Unix","test":"abc\ndef","filler":2}
+{"style":"Mac","test":"abc\rdef","filler":3}
+{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
 -- column list with diverse data types
 create temp table copyjsontest_types (
     id int,
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 404f4321085..bc12ac879ef 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -86,6 +86,8 @@ copy copytest3 to stdout csv header;
 copy (select 1 union all select 2) to stdout with (format json);
 copy (select 1 as foo union all select 2) to stdout with (format json);
 copy (values (1), (2)) TO stdout with (format json);
+copy (select 1 union all select 2) to stdout with (format json, force_array true);
+copy (values (1), (2)) TO stdout with (format json, force_array true);
 copy copytest to stdout json;
 copy copytest to stdout (format json);
 copy (select * from copytest) to stdout (format json);
@@ -109,6 +111,14 @@ copy copytest from stdin(format json);
 -- column list with json format
 copy copytest (style, test, filler) to stdout (format json);
 
+-- should fail: force_array requires json format
+copy copytest to stdout (format csv, force_array true);
+
+-- force_array variants
+copy copytest to stdout (format json, force_array);
+copy copytest(style, test) to stdout (format json, force_array true);
+copy copytest to stdout (format json, force_array false);
+
 -- column list with diverse data types
 create temp table copyjsontest_types (
     id int,
-- 
2.34.1

---

From: Masahiko Sawada <[email-masked]>
Date: Mon, 16 Mar 2026 11:24:58 -0700

> COPY TO with the TEXT and CSV formats.

I've reviewed the patch and have some comments:

---
I got a SEGV in the following scenario:

postgres(1:1197708)=# create table test (a int, b text, c jsonb);
CREATE TABLE
postgres(1:1197708)=# copy test(a, b) to stdout with (format 'json' );
TRAP: failed Assert("tupdesc->firstNonCachedOffsetAttr >= 0"), File:
"execTuples.c", Line: 2328, PID: 1197708
postgres: masahiko postgres [local] COPY(ExceptionalCondition+0x9e) [0xbebe48]
postgres: masahiko postgres [local] COPY(BlessTupleDesc+0x2b) [0x729b50]
postgres: masahiko postgres [local] COPY(BeginCopyTo+0xc94) [0x637bdf]
postgres: masahiko postgres [local] COPY(DoCopy+0xb68) [0x62afbc]
postgres: masahiko postgres [local]
COPY(standard_ProcessUtility+0xa22) [0xa0ba48]
postgres: masahiko postgres [local] COPY(ProcessUtility+0x10e) [0xa0b01f]
postgres: masahiko postgres [local] COPY() [0xa09872]
postgres: masahiko postgres [local] COPY() [0xa09acf]
postgres: masahiko postgres [local] COPY(PortalRun+0x2c8) [0xa0901d]
postgres: masahiko postgres [local] COPY() [0xa02055]
postgres: masahiko postgres [local] COPY(PostgresMain+0xaf1) [0xa0724e]
postgres: masahiko postgres [local] COPY() [0x9fdab9]
postgres: masahiko postgres [local]
COPY(postmaster_child_launch+0x165) [0x905378]
postgres: masahiko postgres [local] COPY() [0x90b600]
postgres: masahiko postgres [local] COPY() [0x908e6a]
postgres: masahiko postgres [local] COPY(PostmasterMain+0x14fe) [0x90880c]
postgres: masahiko postgres [local] COPY(main+0x340) [0x7a1f9c]

It seems to forget to call TupleDescFinalize(). And I think we need
some regression tests for this case.

---

We can conjunct the two if statement conditions.

Regards,

---

From: Andrew Dunstan <[email-masked]>
Date: Mon, 16 Mar 2026 16:59:56 -0400

On 2026-03-16 Mo 2:24 PM, Masahiko Sawada wrote:
> On Sun, Mar 8, 2026 at 8:49 PM jian he<[email-masked]> wrote:
>> On Mon, Mar 9, 2026 at 3:44 AM Andrew Dunstan<[email-masked]> wrote:

Here's a v30 set that I hope fixes these issues.

cheers

andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com
From f05872732a3654362d916354a2edd071aa131099 Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <[email-masked]>
Date: Mon, 16 Mar 2026 16:49:01 -0400
Subject: [PATCH v30 1/3] introduce CopyFormat, refactor CopyFormatOptions

Currently, the COPY command format is determined by two boolean fields
(binary, csv_mode) in CopyFormatOptions.  This approach, while
functional, isn't ideal for implementing other formats in the future.

To simplify adding new formats, introduce a CopyFormat enum.  This makes
the code cleaner and more maintainable, allowing for easier integration
of additional formats down the line.

Author: Joel Jacobson <[email-masked]>
Author: jian he <[email-masked]>
Reviewed-by: Andrew Dunstan <[email-masked]>
Discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
Discussion: https://postgr.es/m/[email-masked]
---
 src/backend/commands/copy.c          | 50 +++++++++++++++-------------
 src/backend/commands/copyfrom.c      |  6 ++--
 src/backend/commands/copyfromparse.c |  7 ++--
 src/backend/commands/copyto.c        |  8 ++---
 src/include/commands/copy.h          | 13 ++++++--
 src/tools/pgindent/typedefs.list     |  1 +
 6 files changed, 49 insertions(+), 36 deletions(-)

 

 

 
 	/* Check header */
 
 	/* Check quote */

 
 	/* Check escape */

 	/* Check force_quote */

 	/* Check force_null */

index 95f6cb416a9..a7fe29a363a 100644
 
 	/* default is text */
index 00ee4154b8b..200d7bc79cd 100644
@@ -174,7 +174,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 
@@ -752,7 +752,7 @@ bool
 
 /*
@@ -779,7 +779,8 @@ NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields
 	bool		done = false;

 
 	/* default is text */

 
 
+/*
index ec8513d90b5..3b2fcebcb54 100644

From 9d13f458dea5c3914705b06c0826c393d02cebcf Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <[email-masked]>
Date: Mon, 16 Mar 2026 16:50:24 -0400
Subject: [PATCH v30 2/3] json format for COPY TO

This introduces the JSON format option for the COPY TO command, allowing
users to export query results or table data directly as a stream of JSON
objects (one per line, NDJSON style).

JSON format is incompatible with some standard text/CSV formatting
options, including HEADER, DEFAULT, NULL, DELIMITER, FORCE QUOTE,
FORCE NOT NULL, and FORCE NULL.

Column list support is included: when a column list is specified, only
the named columns are emitted in each JSON object.

Author: Joe Conway <[email-masked]>
Author: jian he <[email-masked]>
Reviewed-by: Andrey M. Borodin <[email-masked]>
Reviewed-by: Dean Rasheed <[email-masked]>
Reviewed-by: Daniel Verite <[email-masked]>
Reviewed-by: Davin Shearer <[email-masked]>
Reviewed-by: Masahiko Sawada <[email-masked]>
Reviewed-by: Alvaro Herrera <[email-masked]>
Reviewed-by: Junwang Zhao <[email-masked]>
Reviewed-by: Andrew Dunstan <[email-masked]>
Discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
Discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         |  13 ++-
 src/backend/commands/copy.c        |  49 ++++++---
 src/backend/commands/copyto.c      | 162 +++++++++++++++++++++++++++--
 src/backend/parser/gram.y          |   8 ++
 src/backend/utils/adt/json.c       |   5 +-
 src/bin/psql/tab-complete.in.c     |   2 +-
 src/include/commands/copy.h        |   1 +
 src/include/utils/json.h           |   2 +
 src/test/regress/expected/copy.out | 146 ++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      |  88 ++++++++++++++++
 10 files changed, 445 insertions(+), 31 deletions(-)

 
      <note>
index 2f46be516f2..29e22d91ecd 100644

 
 
 	/* Check header */
 
 	/* Check quote */
 
+				errmsg("COPY %s is not supported for %s", "FORMAT JSON", "COPY FROM"));
index b0ee91fc9c1..ffe2268fbb0 100644
 
 	CopyFormatOptions opts;
 
 /*
 
 /* text format */
 
+/* json format */
 
 	/* default is text */

 
 /*

 
 
 /*
 
@@ -886,11 +986,53 @@ BeginCopyTo(ParseState *pstate,

 
+			TupleDescFinalize(resultDesc);
+			 * Pre-allocate arrays for projecting selected column values
 
 	/* Convert FORCE_QUOTE name list to per-column flags, check validity */
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index f01f5734fe9..c01b9fc3997 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -3617,6 +3617,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("format", (Node *) makeString("csv"), @1);
 				}
+			| JSON
+				{
+					$$ = makeDefElem("format", (Node *) makeString("json"), @1);
+				}
 			| HEADER_P
 				{
 					$$ = makeDefElem("header", (Node *) makeBoolean(true), @1);
@@ -3699,6 +3703,10 @@ copy_generic_opt_elem:
 				{
 					$$ = makeDefElem($1, $2, @1);
 				}
+			| FORMAT_LA copy_generic_opt_arg
+				{
+					$$ = makeDefElem("format", $2, @1);
+				}
 		;
 
 copy_generic_opt_arg:

 /*
index 199fc64ddf5..ac36f4591f7 100644

 
 /*
 
index d0d563e0fa8..7f2d2e065f6 100644
+ERROR:  COPY FORMAT JSON is not supported for COPY FROM

From 9e0a65578eb1de9c8d0521b2931fbe76ad5f2bcf Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <[email-masked]>
Date: Mon, 16 Mar 2026 16:51:12 -0400
Subject: [PATCH v30 3/3] Add option force_array for COPY JSON FORMAT

When enabled, this option wraps the output in a top-level JSON array
(enclosed in square brackets with comma-separated elements), making the
entire result a valid single JSON value.  Without this option, the
default behavior is to output a stream of independent JSON objects.

Author: Joe Conway <[email-masked]>
Author: jian he <[email-masked]>
Reviewed-by: Junwang Zhao <[email-masked]>
Reviewed-by: Masahiko Sawada <[email-masked]>
Reviewed-by: Florents Tselai <[email-masked]>
Reviewed-by: Andrew Dunstan <[email-masked]>
Discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com
Discussion: https://postgr.es/m/[email-masked]
---
 doc/src/sgml/ref/copy.sgml         | 30 +++++++++++++++++++++++
 src/backend/commands/copy.c        | 13 ++++++++++
 src/backend/commands/copyto.c      | 38 ++++++++++++++++++++++++++++--
 src/bin/psql/tab-complete.in.c     |  2 +-
 src/include/commands/copy.h        |  1 +
 src/test/regress/expected/copy.out | 37 +++++++++++++++++++++++++++++
 src/test/regress/sql/copy.sql      | 13 ++++++++++
 7 files changed, 131 insertions(+), 3 deletions(-)

 
+<para>
index 29e22d91ecd..e837f417d0d 100644
 
 				errmsg("COPY %s is not supported for %s", "FORMAT JSON", "COPY FROM"));
 
index ffe2268fbb0..12872f04eef 100644
 
 /* binary format */
@@ -248,6 +250,15 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)

 /*
@@ -324,13 +335,24 @@ CopyToTextLikeOneRow(CopyToState cstate,
 	CopySendTextLikeEndOfRow(cstate);
 }

@@ -392,6 +414,18 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)

 
index ac36f4591f7..f44a1f22ebf 100644
 
 /* COPY TO options */
 
 /*
index 7f2d2e065f6..1714faab39c 100644
@@ -134,6 +144,33 @@ copy copytest (style, test, filler) to stdout (format json);
+-- force_array with empty result set
+copy (select 1 where false) to stdout (format json, force_array);
index 404f4321085..eaad290b257 100644
@@ -109,6 +111,17 @@ copy copytest from stdin(format json);
 
+-- should fail: force_array requires json format
+copy copytest to stdout (format csv, force_array true);
+
+-- force_array variants
+copy copytest to stdout (format json, force_array);
+copy copytest(style, test) to stdout (format json, force_array true);
+copy copytest to stdout (format json, force_array false);
+
+-- force_array with empty result set
+copy (select 1 where false) to stdout (format json, force_array);
+
 -- column list with diverse data types
 create temp table copyjsontest_types (
     id int,
-- 
2.43.0

---

From: Masahiko Sawada <[email-masked]>
Date: Tue, 17 Mar 2026 10:50:35 -0700

> Here's a v30 set that I hope fixes these issues.

Thank you for updating the patch! The patches look good to me.

Regards,

---

From: "Daniel Verite" <[email-masked]>
Date: Wed, 18 Mar 2026 15:37:23 +0100

> Here's a v30 set that I hope fixes these issues.

Currently there's no difference in output between the null
json value and the SQL null.

postgres=# create table tbl  (j jsonb);
CREATE TABLE

postgres=# insert into tbl values('null');
INSERT 0 1

postgres=# insert into tbl values(null);
INSERT 0 1

postgres=# table tbl;
  j   
------
 null
 
(2 rows)

postgres=# copy tbl to stdout with (format json);
{"j":null}
{"j":null}

If we had to reload this file, we could not determine which
kind of null we had even though they are different at the SQL
level:

postgres=# select null::jsonb is distinct from 'null'::jsonb;
 ?column? 
----------
 t

Does it have to be that way or are there valid distinct outputs
that  we could use to avoid this ambiguity?

Best regards,
-- 
Daniel Vérité 
https://postgresql.verite.pro/

---

From: jian he <[email-masked]>
Date: Thu, 19 Mar 2026 09:58:05 +0800

> that  we could use to avoid this ambiguity?

This is an existing (quite old) behavior of
composite_to_json->datum_to_json_internal, IMHO.

```
    if (is_null)
    {
        appendBinaryStringInfo(result, "null", strlen("null"));
        return;
    }
```
produce the same results as
```
case JSONTYPE_JSON:
    /* JSON and JSONB output will already be escaped */
    outputstr = OidOutputFunctionCall(outfuncoid, val);
    appendStringInfoString(result, outputstr);
    pfree(outputstr);
    break;
```

Therefore I intended to document it as below:

  <refsect2 id="sql-copy-json-format" xreflabel="JSON Format">
   <title>JSON Format</title>
    <para>
      When the <literal>json</literal> format is used, data is
exported with one JSON object per line,
      where each line corresponds to a single record.
      The <literal>json</literal> format has no standard way to
distinguish between an SQL <literal>NULL</literal> and a JSON
<literal>null</literal> literal.
      In the examples that follow, the following table containing JSON
data will be used:
<programlisting>
CREATE TABLE my_test (a jsonb, b int);
INSERT INTO my_test VALUES ('null', 1), (NULL, 1);
</programlisting>

    When exporting this table using the <literal>json</literal> format:
<programlisting>
COPY my_test TO STDOUT (FORMAT JSON);
</programlisting>
    In the resulting output, both the SQL <literal>NULL</literal> and
the JSON <literal>null</literal> are rendered identically:
<screen>
{"a":null,"b":1}
{"a":null,"b":1}
</screen>
   </para>
  </refsect2>

what do you think?

---

From: Andrew Dunstan <[email-masked]>
Date: Thu, 19 Mar 2026 11:02:21 -0400

> the JSON <literal>null</literal> are rendered identically:

I can live with that, if others can.

cheers

andrew

---

From: Joe Conway <[email-masked]>
Date: Thu, 19 Mar 2026 12:06:13 -0400

> I can live with that, if others can.

+1
WFM

-- 
Joe Conway
PostgreSQL Contributors Team
Amazon Web Services: https://aws.amazon.com