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, 10 insertions, 11 deletions

diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 2b04ee5e337..79b45414d47 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_clause.c,v 1.174 2008/08/05 02:43:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_clause.c,v 1.175 2008/08/07 01:11:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -70,6 +70,9 @@ static List *addTargetToSortList(ParseState *pstate, TargetEntry *tle,
 					List *sortlist, List *targetlist,
 					SortByDir sortby_dir, SortByNulls sortby_nulls,
 					List *sortby_opname, bool resolveUnknown);
+static List *addTargetToGroupList(ParseState *pstate, TargetEntry *tle,
+					 List *grouplist, List *targetlist,
+					 bool resolveUnknown);
 
 
 /*
@@ -1355,7 +1358,7 @@ transformGroupClause(ParseState *pstate, List *grouplist,
 		if (!found)
 			result = addTargetToGroupList(pstate, tle,
 										  result, *targetlist,
-										  false, true);
+										  true);
 	}
 
 	return result;
@@ -1456,7 +1459,7 @@ transformDistinctClause(ParseState *pstate,
 			continue;			/* ignore junk */
 		result = addTargetToGroupList(pstate, tle,
 									  result, *targetlist,
-									  false, true);
+									  true);
 	}
 
 	return result;
@@ -1551,7 +1554,7 @@ transformDistinctOnClause(ParseState *pstate, List *distinctlist,
 					 errmsg("SELECT DISTINCT ON expressions must match initial ORDER BY expressions")));
 		result = addTargetToGroupList(pstate, tle,
 									  result, *targetlist,
-									  false, true);
+									  true);
 	}
 
 	return result;
@@ -1679,10 +1682,6 @@ addTargetToSortList(ParseState *pstate, TargetEntry *tle,
  * the TLE is considered "already in the list" if it appears there with any
  * sorting semantics.
  *
- * If requireSortOp is TRUE, we require a sorting operator to be found too.
- * XXX this argument should eventually be obsolete, but for now there are
- * parts of the system that can't support non-sortable grouping lists.
- *
  * If resolveUnknown is TRUE, convert TLEs of type UNKNOWN to TEXT.  If not,
  * do nothing (which implies the search for an equality operator will fail).
  * pstate should be provided if resolveUnknown is TRUE, but can be NULL
@@ -1690,10 +1689,10 @@ addTargetToSortList(ParseState *pstate, TargetEntry *tle,
  *
  * Returns the updated SortGroupClause list.
  */
-List *
+static List *
 addTargetToGroupList(ParseState *pstate, TargetEntry *tle,
 					 List *grouplist, List *targetlist,
-					 bool requireSortOp, bool resolveUnknown)
+					 bool resolveUnknown)
 {
 	Oid			restype = exprType((Node *) tle->expr);
 	Oid			sortop;
@@ -1716,7 +1715,7 @@ addTargetToGroupList(ParseState *pstate, TargetEntry *tle,
 
 		/* determine the eqop and optional sortop */
 		get_sort_group_operators(restype,
-								 requireSortOp, true, false,
+								 false, true, false,
 								 &sortop, &eqop, NULL);
 
 		grpcl->tleSortGroupRef = assignSortGroupRef(tle, targetlist);