Fix estimate_num_groups() to not fail on PlaceHolderVars, per report from

Stefan Kaltenbrunner.  The most reasonable behavior (at least for the near
term) seems to be to ignore the PlaceHolderVar and examine its argument
instead.  In support of this, change the API of pull_var_clause() to allow
callers to request recursion into PlaceHolderVars.  Currently
estimate_num_groups() is the only customer for that behavior, but where
there's one there may be others.

1 files changed, 24 insertions, 14 deletions

diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index 7768712b569..cd88c337f1a 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/var.c,v 1.84 2009/02/25 03:30:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/var.c,v 1.85 2009/04/19 19:46:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -56,7 +56,7 @@ typedef struct
 typedef struct
 {
 	List	   *varlist;
-	bool		includePlaceHolderVars;
+	PVCPlaceHolderBehavior behavior;
 } pull_var_clause_context;
 
 typedef struct
@@ -614,11 +614,13 @@ find_minimum_var_level_walker(Node *node,
  * pull_var_clause
  *	  Recursively pulls all Var nodes from an expression clause.
  *
- *	  PlaceHolderVars are included too, if includePlaceHolderVars is true.
- *	  If it isn't true, an error is thrown if any are found.
- *	  Note that Vars within a PHV's expression are *not* included.
+ *	  PlaceHolderVars are handled according to 'behavior':
+ *		PVC_REJECT_PLACEHOLDERS		throw error if PlaceHolderVar found
+ *		PVC_INCLUDE_PLACEHOLDERS	include PlaceHolderVars in output list
+ *		PVC_RECURSE_PLACEHOLDERS	recurse into PlaceHolderVar argument
+ *	  Vars within a PHV's expression are included only in the last case.
  *
- *	  CurrentOfExpr nodes are *not* included.
+ *	  CurrentOfExpr nodes are ignored in all cases.
  *
  *	  Upper-level vars (with varlevelsup > 0) are not included.
  *	  (These probably represent errors too, but we don't complain.)
@@ -630,12 +632,12 @@ find_minimum_var_level_walker(Node *node,
  * of sublinks to subplans!
  */
 List *
-pull_var_clause(Node *node, bool includePlaceHolderVars)
+pull_var_clause(Node *node, PVCPlaceHolderBehavior behavior)
 {
 	pull_var_clause_context context;
 
 	context.varlist = NIL;
-	context.includePlaceHolderVars = includePlaceHolderVars;
+	context.behavior = behavior;
 
 	pull_var_clause_walker(node, &context);
 	return context.varlist;
@@ -654,12 +656,20 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
 	}
 	if (IsA(node, PlaceHolderVar))
 	{
-		if (!context->includePlaceHolderVars)
-			elog(ERROR, "PlaceHolderVar found where not expected");
-		if (((PlaceHolderVar *) node)->phlevelsup == 0)
-			context->varlist = lappend(context->varlist, node);
-		/* we do NOT descend into the contained expression */
-		return false;
+		switch (context->behavior)
+		{
+			case PVC_REJECT_PLACEHOLDERS:
+				elog(ERROR, "PlaceHolderVar found where not expected");
+				break;
+			case PVC_INCLUDE_PLACEHOLDERS:
+				if (((PlaceHolderVar *) node)->phlevelsup == 0)
+					context->varlist = lappend(context->varlist, node);
+				/* we do NOT descend into the contained expression */
+				return false;
+			case PVC_RECURSE_PLACEHOLDERS:
+				/* ignore the placeholder, look at its argument instead */
+				break;
+		}
 	}
 	return expression_tree_walker(node, pull_var_clause_walker,
 								  (void *) context);