Teach the system how to use hashing for UNION. (INTERSECT/EXCEPT will follow,

but seem like a separate patch since most of the remaining work is on the
executor side.)  I took the opportunity to push selection of the grouping
operators for set operations into the parser where it belongs.  Otherwise this
is just a small exercise in making prepunion.c consider both alternatives.

As with the recent DISTINCT patch, this means we can UNION on datatypes that
can hash but not sort, and it means that UNION without ORDER BY is no longer
certain to produce sorted output.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/include/optimizer/tlist.h b/src/include/optimizer/tlist.h
index 8a8966213b..9899b14c82 100644
--- a/src/include/optimizer/tlist.h
+++ b/src/include/optimizer/tlist.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/tlist.h,v 1.50 2008/08/02 21:32:01 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/tlist.h,v 1.51 2008/08/07 01:11:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,6 +32,11 @@ extern Node *get_sortgroupclause_expr(SortGroupClause *sgClause,
 extern List *get_sortgrouplist_exprs(List *sgClauses,
 						List *targetList);
 
+extern Oid *extract_grouping_ops(List *groupClause);
+extern AttrNumber *extract_grouping_cols(List *groupClause, List *tlist);
+extern bool grouping_is_sortable(List *groupClause);
+extern bool grouping_is_hashable(List *groupClause);
+
 extern bool tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK);
 
 #endif   /* TLIST_H */