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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2003-01-06 01:20:40 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2003-01-06 01:20:40 +0000 |
| commit | d99e7b5a0dc15f86bc9a66de315bf5ed6f7c5271 (patch) | |
| tree | af8bd0251118601d39dbb04a1ded6956ed5c62cb /doc/src | |
| parent | daec989f6a763c9353ba2912b92f5b03c0246c1f (diff) | |
| download | postgresql-d99e7b5a0dc15f86bc9a66de315bf5ed6f7c5271.tar.gz postgresql-d99e7b5a0dc15f86bc9a66de315bf5ed6f7c5271.zip | |
Add note explaining that a mergejoinable equality operator is now
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.
Diffstat (limited to 'doc/src')
| -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 |