Date: Sat, 28 Oct 2023 21:47:03 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, rjuju123@gmail.com,
	pgsql-hackers@postgresql.org
Subject: Re: COPY TO (FREEZE)?
Message-ID: <ZT25lzyz3T8YA7mM@momjian.us>
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On Sat, Oct 28, 2023 at 09:39:53PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > My apologies, wrong patch attached, right one attached now.
> 
> I think this one is fine as-is:
> 
>  	/* Only single-byte delimiter strings are supported. */
>  	if (strlen(opts_out->delim) != 1)
>  		ereport(ERROR,
> -				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> +				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
>  				 errmsg("COPY delimiter must be a single one-byte character")));
>  
> While we have good implementation reasons for this restriction,
> there's nothing illogical about wanting the delimiter to be more
> general.  It's particularly silly, from an end-user's standpoint,
> that for example 'é' is an allowed delimiter in LATIN1 encoding
> but not when the server is using UTF8.  So I don't see how the
> distinction you presented justifies this change.

Agreed, my mistake.
 
> +	if (opts_out->freeze && !is_from)
> +		ereport(ERROR,
> +				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> +				 errmsg("COPY freeze only available using COPY FROM")));
> 
> Not thrilled by the wording here.  I don't like the fact that the
> keyword FREEZE isn't capitalized, and I think you omitted too many
> words for intelligibility to be preserved.  Notably, all the adjacent
> examples use "must" or "must not", and this decides that that can be
> omitted.

I think it is modeled after:

	errmsg("COPY force null only available using COPY FROM")));

> I realize that you probably modeled the non-capitalization on nearby
> messages like "COPY delimiter", but there's a difference IMO:
> "delimiter" can be read as an English noun, but it's hard to read
> "freeze" as a noun.
> 
> How about, say,
> 
> 	errmsg("COPY FREEZE must not be used in COPY TO")));
> 
> or perhaps that's redundant and we could write
> 
> 	errmsg("FREEZE option must not be used in COPY TO")));

I now have:

	errmsg("COPY FREEZE mode only available using COPY FROM")));

Updated patch attached.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Only you can decide what is important to you.

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diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index d12ba96497..82b65543c3 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -224,6 +224,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       open and there are no older snapshots held by this transaction.  It is
       currently not possible to perform a <command>COPY FREEZE</command> on
       a partitioned table.
+      This option is allowed only in <command>COPY FROM</command>.
      </para>
      <para>
       Note that all other sessions will immediately be able to see the data
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index c5d7d78645..92558b6bb0 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -728,16 +728,22 @@ ProcessCopyOptions(ParseState *pstate,
 	/* Don't allow the delimiter to appear in the null string. */
 	if (strchr(opts_out->null_print, opts_out->delim[0]) != NULL)
 		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("COPY delimiter must not appear in the NULL specification")));
 
 	/* Don't allow the CSV quote char to appear in the null string. */
 	if (opts_out->csv_mode &&
 		strchr(opts_out->null_print, opts_out->quote[0]) != NULL)
 		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("CSV quote character must not appear in the NULL specification")));
 
+	/* Check freeze */
+	if (opts_out->freeze && !is_from)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("COPY FREEZE mode only available using COPY FROM")));
+
 	if (opts_out->default_print)
 	{
 		if (!is_from)

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