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, 12 insertions, 17 deletions

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index ad3c10ac27b..655443e9efe 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.144 2008/08/02 21:32:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.145 2008/08/07 01:11:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,7 +24,6 @@
 #include "optimizer/paths.h"
 #include "optimizer/tlist.h"
 #include "parser/parse_expr.h"
-#include "parser/parse_oper.h"
 #include "parser/parsetree.h"
 #include "utils/selfuncs.h"
 #include "utils/lsyscache.h"
@@ -1003,12 +1002,6 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
 	/*
 	 * UNION, INTERSECT, EXCEPT guarantee uniqueness of the whole output row,
 	 * except with ALL.
-	 *
-	 * XXX this code knows that prepunion.c will adopt the default sort/group
-	 * operators for each column datatype to determine uniqueness.  It'd
-	 * probably be better if these operators were chosen at parse time and
-	 * stored into the parsetree, instead of leaving bits of the planner to
-	 * decide semantics.
 	 */
 	if (query->setOperations)
 	{
@@ -1019,24 +1012,26 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
 
 		if (!topop->all)
 		{
+			ListCell   *lg;
+
 			/* We're good if all the nonjunk output columns are in colnos */
+			lg = list_head(topop->groupClauses);
 			foreach(l, query->targetList)
 			{
 				TargetEntry *tle = (TargetEntry *) lfirst(l);
-				Oid		tle_eq_opr;
+				SortGroupClause *sgc;
 
 				if (tle->resjunk)
 					continue;	/* ignore resjunk columns */
 
+				/* non-resjunk columns should have grouping clauses */
+				Assert(lg != NULL);
+				sgc = (SortGroupClause *) lfirst(lg);
+				lg = lnext(lg);
+
 				opid = distinct_col_search(tle->resno, colnos, opids);
-				if (!OidIsValid(opid))
-					break;		/* exit early if no match */
-				/* check for compatible semantics */
-				get_sort_group_operators(exprType((Node *) tle->expr),
-										 false, false, false,
-										 NULL, &tle_eq_opr, NULL);
-				if (!OidIsValid(tle_eq_opr) ||
-					!equality_ops_are_compatible(opid, tle_eq_opr))
+				if (!OidIsValid(opid) ||
+					!equality_ops_are_compatible(opid, sgc->eqop))
 					break;		/* exit early if no match */
 			}
 			if (l == NULL)		/* had matches for all? */