From acde8b3cab4826149177b2cbd3c067867a5b0a0a Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 10 Apr 2005 20:57:32 +0000
Subject: [PATCH] Make constant-folding produce sane output for
 COALESCE(NULL,NULL), that is a plain NULL and not a COALESCE with no inputs. 
 Fixes crash reported by Michael Williamson.

---
 src/backend/optimizer/util/clauses.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 24d74523c3..926162d469 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.193 2005/04/06 16:34:06 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.194 2005/04/10 20:57:32 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1788,6 +1788,10 @@ eval_const_expressions_mutator(Node *node,
 			newargs = lappend(newargs, e);
 		}
 
+		/* If all the arguments were constant null, the result is just null */
+		if (newargs == NIL)
+			return (Node *) makeNullConst(coalesceexpr->coalescetype);
+
 		newcoalesce = makeNode(CoalesceExpr);
 		newcoalesce->coalescetype = coalesceexpr->coalescetype;
 		newcoalesce->args = newargs;