From c531737641b7c0951b29b80144362168d1f96aa1 Mon Sep 17 00:00:00 2001 From: jian he Date: Fri, 6 Mar 2026 17:30:23 +0800 Subject: [PATCH v26 4/4] COPY TO JSON support column lists Author: Andrew Dunstan Reviewed-by: jian he discussion: https://postgr.es/m/CALvfUkBxTYy5uWPFVwpk_7ii2zgT07t3d-yR_cy4sfrrLU%3Dkcg%40mail.gmail.com discussion: https://postgr.es/m/6a04628d-0d53-41d9-9e35-5a8dc302c34c@joeconway.com --- 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); +-- column list with json format +copy copytest (style, filler) to stdout (format json); +copy copytest (style, filler) to stdout (format json, force_array true); + -- embedded escaped characters create temp table copyjsontest ( id bigserial, -- 2.34.1