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Diffstat (limited to 'doc/src/sgml/xoper.sgml')
| -rw-r--r-- | doc/src/sgml/xoper.sgml | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/doc/src/sgml/xoper.sgml b/doc/src/sgml/xoper.sgml index 395306bbd60..24c74cd8b60 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 1.21 2003/01/06 01:20:40 tgl Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.22 2003/01/15 19:35:35 tgl Exp $ --> <Chapter Id="xoper"> @@ -375,6 +375,27 @@ table1.column1 OP table2.column2 equality operators that are (or could be) implemented by <function>memcmp()</function>. </para> + <note> + <para> + The function underlying a hashjoinable operator must be marked + immutable or stable. If it is volatile, the system will never + attempt to use the operator for a hash join. + </para> + </note> + + <note> + <para> + If a hashjoinable operator has an underlying function that is marked + strict, the + function must also be complete: that is, it should return TRUE or + FALSE, never NULL, for any two non-NULL inputs. If this rule is + not followed, hash-optimization of <literal>IN</> operations may + generate wrong results. (Specifically, <literal>IN</> might return + FALSE where the correct answer per spec would be NULL; or it might + yield an error complaining that it wasn't prepared for a NULL result.) + </para> + </note> + </sect2> <sect2> @@ -474,6 +495,14 @@ table1.column1 OP table2.column2 <note> <para> + The function underlying a mergejoinable operator must be marked + immutable or stable. If it is volatile, the system will never + attempt to use the operator for a merge join. + </para> + </note> + + <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 |