diff options
Diffstat (limited to 'src/backend/parser/parse_clause.c')
| -rw-r--r-- | src/backend/parser/parse_clause.c | 41 |
1 files changed, 31 insertions, 10 deletions
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c index a29eb007fb7..2e2beabddcb 100644 --- a/src/backend/parser/parse_clause.c +++ b/src/backend/parser/parse_clause.c @@ -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)) - { - GroupClause *grpcl = makeNode(GroupClause); - - grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist); - - grpcl->sortop = ordering_oper_opid(tle->resdom->restype); + if (targetIsInSortList(tle, glist)) + continue; - glist = lappend(glist, grpcl); + /* + * 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) + { + 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; |