transformColumnDefinition failed to complain about

	create table foo (bar int default null default 3);
due to not thinking about the special-case handling of DEFAULT NULL.
Problem noticed while investigating bug #3396.

Author: tglsfdc

src/backend/parser/analyze.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.253.2.2 2003/02/13 22:50:09 tgl Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.253.2.3 2007/06/20 18:21:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -793,6 +793,7 @@ transformColumnDefinition(ParseState *pstate, CreateStmtContext *cxt,
 {
 	bool		is_serial;
 	bool		saw_nullable;
+	bool		saw_default;
 	Constraint *constraint;
 	List	   *clist;
 
@@ -895,6 +896,7 @@ transformColumnDefinition(ParseState *pstate, CreateStmtContext *cxt,
 	transformConstraintAttrs(column->constraints);
 
 	saw_nullable = false;
+	saw_default = false;
 
 	foreach(clist, column->constraints)
 	{
@@ -935,11 +937,13 @@ transformColumnDefinition(ParseState *pstate, CreateStmtContext *cxt,
 				break;
 
 			case CONSTR_DEFAULT:
-				if (column->raw_default != NULL)
+				if (saw_default)
 					elog(ERROR, "%s/DEFAULT multiple values specified for '%s.%s'",
 						 cxt->stmtType, cxt->relation->relname, column->colname);
+				/* Note: DEFAULT NULL maps to constraint->raw_expr == NULL */
 				column->raw_default = constraint->raw_expr;
 				Assert(constraint->cooked_expr == NULL);
+				saw_default = true;
 				break;
 
 			case CONSTR_PRIMARY: