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Cause GROUP BY clause to adopt ordering operators from ORDER BY when

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both clauses specify the same targets, rather than always using the
default ordering operator.  This allows 'GROUP BY foo ORDER BY foo DESC'
to be done with only one sort step.
This commit is contained in:
Tom Lane
2003-06-15 16:42:08 +00:00
parent da78e3e2eb
commit 996fdb9af1
3 changed files with 43 additions and 17 deletions
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41
src/backend/parser/parse_clause.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.114 2003/06/06 15:04:02 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.115 2003/06/15 16:42:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1124,7 +1124,8 @@ findTargetlistEntry(ParseState *pstate, Node *node, List *tlist, int clause)
* transform a GROUP BY clause
*/
List *
transformGroupClause(ParseState *pstate, List *grouplist, List *targetlist)
transformGroupClause(ParseState *pstate, List *grouplist,
List *targetlist, List *sortClause)
{
List *glist = NIL,
*gl;
@ -1132,21 +1133,41 @@ transformGroupClause(ParseState *pstate, List *grouplist, List *targetlist)
foreach(gl, grouplist)
{
TargetEntry *tle;
Oid ordering_op;
GroupClause *grpcl;
tle = findTargetlistEntry(pstate, lfirst(gl),
targetlist, GROUP_CLAUSE);
/* avoid making duplicate grouplist entries */
if (!targetIsInSortList(tle, glist))
if (targetIsInSortList(tle, glist))
continue;
/*
* If the GROUP BY clause matches the ORDER BY clause, we want to
* adopt the ordering operators from the latter rather than using
* the default ops. This allows "GROUP BY foo ORDER BY foo DESC" to
* be done with only one sort step. Note we are assuming that any
* user-supplied ordering operator will bring equal values together,
* which is all that GROUP BY needs.
*/
if (sortClause &&
((SortClause *) lfirst(sortClause))->tleSortGroupRef ==
tle->resdom->ressortgroupref)
{
GroupClause *grpcl = makeNode(GroupClause);
grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
grpcl->sortop = ordering_oper_opid(tle->resdom->restype);
glist = lappend(glist, grpcl);
ordering_op = ((SortClause *) lfirst(sortClause))->sortop;
sortClause = lnext(sortClause);
}
else
{
ordering_op = ordering_oper_opid(tle->resdom->restype);
sortClause = NIL; /* disregard ORDER BY once match fails */
}
grpcl = makeNode(GroupClause);
grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
grpcl->sortop = ordering_op;
glist = lappend(glist, grpcl);
}
return glist;