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Remove pre-7.3 mention that FOR UPDATE can be before LIMIT.

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Document that FOR UPDATE and LIMIT together can return fewer rows that
LIMIT specifies, and why.
This commit is contained in:
Bruce Momjian 2005-04-22 04:20:44 +00:00
parent 26bb65df1e
commit d76f279a55
1 changed files with 8 additions and 6 deletions
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14
doc/src/sgml/ref/select.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.83 2005/04/08 00:59:58 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.84 2005/04/22 04:20:44 momjian Exp $
PostgreSQL documentation
-->
@ -830,11 +830,13 @@ FOR UPDATE [ OF <replaceable class="parameter">table_name</replaceable> [, ...]
</para>
<para>
<literal>FOR UPDATE</literal> may appear before
<literal>LIMIT</literal> for compatibility with
<productname>PostgreSQL</productname> versions before 7.3. It
effectively executes after <literal>LIMIT</literal>, however, and
so that is the recommended place to write it.
It is possible for a <command>SELECT</> command using both
<literal>LIMIT</literal> and <literal>FOR UPDATE</literal>
clauses to return fewer rows than specified by <literal>LIMIT</literal>.
This is because <literal>LIMIT</> selects a number of rows,
but might then block requesting a <literal>FOR UPDATE</literal> lock.
Once the <literal>SELECT</> unblocks, the query qualifiation might not
be met and the row not be returned by <literal>SELECT</>.
</para>
</refsect2>
</refsect1>