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.

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 24d74523c3713532d015f9d0f9e78a69f7d475c7..926162d469cb6f6d2461c1c11fa1a3c6fcc03057 100644 (file)
--- 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;