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Add note explaining that a mergejoinable equality operator is now

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required if a datatype is to be accepted by GROUP BY, DISTINCT, or
ORDER BY.  This is documentation for code changes made pursuant to
pgsql-hackers discussion around 29-Nov-02.
This commit is contained in:
Tom Lane 2003-01-06 01:20:40 +00:00
parent daec989f6a
commit d99e7b5a0d
1 changed files with 12 additions and 1 deletions
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13
doc/src/sgml/xoper.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.20 2002/09/21 18:32:54 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.21 2003/01/06 01:20:40 tgl Exp $
-->
<Chapter Id="xoper">
@ -472,6 +472,17 @@ table1.column1 OP table2.column2
</itemizedlist>
</para>
<note>
<para>
<literal>GROUP BY</> and <literal>DISTINCT</> operations require each
datatype being grouped or compared to have a mergejoinable
equality operator named <literal>=</>. The equality operator and its
associated <literal>SORT1</> operator are used to implement these
operations. Also, the associated <literal>SORT1</> operator is the
default ordering operator for <literal>ORDER BY</>.
</para>
</note>
<note>
<para>
In <ProductName>PostgreSQL</ProductName> versions before 7.3,