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, 105 insertions, 1 deletions

diff --git a/src/backend/optimizer/util/tlist.c b/src/backend/optimizer/util/tlist.c
index fc0880ad56..a2c627fd4d 100644
--- a/src/backend/optimizer/util/tlist.c
+++ b/src/backend/optimizer/util/tlist.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.79 2008/08/02 21:32:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.80 2008/08/07 01:11:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,6 +18,7 @@
 #include "optimizer/tlist.h"
 #include "optimizer/var.h"
 #include "parser/parse_expr.h"
+#include "utils/lsyscache.h"
 
 
 /*****************************************************************************
@@ -202,6 +203,109 @@ get_sortgrouplist_exprs(List *sgClauses, List *targetList)
 }
 
 
+/*****************************************************************************
+ *		Functions to extract data from a list of SortGroupClauses
+ *
+ * These don't really belong in tlist.c, but they are sort of related to the
+ * functions just above, and they don't seem to deserve their own file.
+ *****************************************************************************/
+
+/*
+ * extract_grouping_ops - make an array of the equality operator OIDs
+ *		for a SortGroupClause list
+ */
+Oid *
+extract_grouping_ops(List *groupClause)
+{
+	int			numCols = list_length(groupClause);
+	int			colno = 0;
+	Oid		   *groupOperators;
+	ListCell   *glitem;
+
+	groupOperators = (Oid *) palloc(sizeof(Oid) * numCols);
+
+	foreach(glitem, groupClause)
+	{
+		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);
+
+		groupOperators[colno] = groupcl->eqop;
+		Assert(OidIsValid(groupOperators[colno]));
+		colno++;
+	}
+
+	return groupOperators;
+}
+
+/*
+ * extract_grouping_cols - make an array of the grouping column resnos
+ *		for a SortGroupClause list
+ */
+AttrNumber *
+extract_grouping_cols(List *groupClause, List *tlist)
+{
+	AttrNumber *grpColIdx;
+	int			numCols = list_length(groupClause);
+	int			colno = 0;
+	ListCell   *glitem;
+
+	grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
+
+	foreach(glitem, groupClause)
+	{
+		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);
+		TargetEntry *tle = get_sortgroupclause_tle(groupcl, tlist);
+
+		grpColIdx[colno++] = tle->resno;
+	}
+
+	return grpColIdx;
+}
+
+/*
+ * grouping_is_sortable - is it possible to implement grouping list by sorting?
+ *
+ * This is easy since the parser will have included a sortop if one exists.
+ */
+bool
+grouping_is_sortable(List *groupClause)
+{
+	ListCell   *glitem;
+
+	foreach(glitem, groupClause)
+	{
+		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);
+
+		if (!OidIsValid(groupcl->sortop))
+			return false;
+	}
+	return true;
+}
+
+/*
+ * grouping_is_hashable - is it possible to implement grouping list by hashing?
+ *
+ * We assume hashing is OK if the equality operators are marked oprcanhash.
+ * (If there isn't actually a supporting hash function, the executor will
+ * complain at runtime; but this is a misdeclaration of the operator, not
+ * a system bug.)
+ */
+bool
+grouping_is_hashable(List *groupClause)
+{
+	ListCell   *glitem;
+
+	foreach(glitem, groupClause)
+	{
+		SortGroupClause *groupcl = (SortGroupClause *) lfirst(glitem);
+
+		if (!op_hashjoinable(groupcl->eqop))
+			return false;
+	}
+	return true;
+}
+
+
+
 /*
  * Does tlist have same output datatypes as listed in colTypes?
  *