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 c6057687b8f2bad6bf6467b625d704e6483d641b..a43256cc1f27242ae80ada5b528dc3b0cb42fb73 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 1.186.4.2 2005/02/02 21:49:43 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.186.4.3 2005/04/10 20:57:45 tgl Exp $
  *
  * HISTORY
  *       AUTHOR                        DATE                    MAJOR EVENT
@@ -1771,6 +1771,10 @@ 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;