Suppress subquery pullup/pushdown when a subquery contains volatile

tglsfdc · tglsfdc · commit fb9e56eea11a · 2006-08-19T02:48:53.000Z
functions in its targetlist, to avoid introducing multiple evaluations
of volatile functions that textually appear only once.  This is a
slightly tighter version of Jaime Casanova's recent patch.
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.151 2006/08/10 02:36:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.152 2006/08/19 02:48:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -871,6 +871,10 @@ compare_tlist_datatypes(List *tlist, List *colTypes,
  * 5. We must not push down any quals that refer to subselect outputs that
  * return sets, else we'd introduce functions-returning-sets into the
  * subquery's WHERE/HAVING quals.
+ *
+ * 6. We must not push down any quals that refer to subselect outputs that
+ * contain volatile functions, for fear of introducing strange results due
+ * to multiple evaluation of a volatile function.
  */
 static bool
 qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
@@ -940,6 +944,13 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
 			safe = false;
 			break;
 		}
+
+		/* Refuse volatile functions (point 6) */
+		if (contain_volatile_functions((Node *) tle->expr))
+		{
+			safe = false;
+			break;
+		}
 	}
 
 	list_free(vars);
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.42 2006/08/12 20:05:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.43 2006/08/19 02:48:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -656,6 +656,15 @@ is_simple_subquery(Query *subquery)
 	if (expression_returns_set((Node *) subquery->targetList))
 		return false;
 
+	/*
+	 * Don't pull up a subquery that has any volatile functions in its
+	 * targetlist.  Otherwise we might introduce multiple evaluations of
+	 * these functions, if they get copied to multiple places in the upper
+	 * query, leading to surprising results.
+	 */
+	if (contain_volatile_functions((Node *) subquery->targetList))
+		return false;
+
 	/*
 	 * Hack: don't try to pull up a subquery with an empty jointree.
 	 * query_planner() will correctly generate a Result plan for a jointree
