Implement outer-level aggregates to conform to the SQL spec, with

extensions to support our historical behavior.  An aggregate belongs
to the closest query level of any of the variables in its argument,
or the current query level if there are no variables (e.g., COUNT(*)).
The implementation involves adding an agglevelsup field to Aggref,
and treating outer aggregates like outer variables at planning time.

src/include/nodes/primnodes.h

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: primnodes.h,v 1.82 2003/05/06 00:20:33 tgl Exp $
+ * $Id: primnodes.h,v 1.83 2003/06/06 15:04:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -223,6 +223,7 @@ typedef struct Aggref
 	Oid			aggfnoid;		/* pg_proc Oid of the aggregate */
 	Oid			aggtype;		/* type Oid of result of the aggregate */
 	Expr	   *target;			/* expression we are aggregating on */
+	Index		agglevelsup;	/* > 0 if agg belongs to outer query */
 	bool		aggstar;		/* TRUE if argument was really '*' */
 	bool		aggdistinct;	/* TRUE if it's agg(DISTINCT ...) */
 } Aggref;