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| -rw-r--r-- | doc/src/sgml/xoper.sgml | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/doc/src/sgml/xoper.sgml b/doc/src/sgml/xoper.sgml index 23db99705f7..395306bbd60 100644 --- a/doc/src/sgml/xoper.sgml +++ b/doc/src/sgml/xoper.sgml @@ -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"> @@ -474,6 +474,17 @@ table1.column1 OP table2.column2 <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, the <literal>MERGES</> shorthand was not available: to make a merge-joinable operator one had to write both <literal>SORT1</> and |