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 24d7452..926162d 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;