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Fix psql's "\g target" meta-command to work with COPY TO STDOUT.

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Previously, \g would successfully execute the COPY command, but
the target specification if any was ignored, so that the data was
always dumped to the regular query output target.  This seems like
a clear bug, so let's not just fix it but back-patch it.

While at it, adjust the documentation for \copy to recommend
"COPY ... TO STDOUT \g foo" as a plausible alternative.

Back-patch to 9.5.  The problem exists much further back, but the
code associated with \g was refactored enough in 9.5 that we'd
need a significantly different patch for 9.4, and it doesn't
seem worth the trouble.

Daniel Vérité, reviewed by Fabien Coelho

Discussion: https://postgr.es/m/15dadc39-e050-4d46-956b-dcc4ed098753@manitou-mail.org
This commit is contained in:
Tom Lane
2019-01-26 14:15:42 -05:00
parent 741ee48900
commit cda1e27fb7
3 changed files with 73 additions and 13 deletions
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22
doc/src/sgml/ref/psql-ref.sgml
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@ -958,10 +958,24 @@ testdb=>
<tip>
<para>
This operation is not as efficient as the <acronym>SQL</acronym>
<command>COPY</command> command because all data must pass
through the client/server connection. For large
amounts of data the <acronym>SQL</acronym> command might be preferable.
Another way to obtain the same result as <literal>\copy
... to</literal> is to use the <acronym>SQL</acronym> <literal>COPY
... TO STDOUT</literal> command and terminate it
with <literal>\g <replaceable>filename</replaceable></literal>
or <literal>\g |<replaceable>program</replaceable></literal>.
Unlike <literal>\copy</literal>, this method allows the command to
span multiple lines; also, variable interpolation and backquote
expansion can be used.
</para>
</tip>
<tip>
<para>
These operations are not as efficient as the <acronym>SQL</acronym>
<command>COPY</command> command with a file or program data source or
destination, because all data must pass through the client/server
connection. For large amounts of data the <acronym>SQL</acronym>
command might be preferable.
</para>
</tip>