Restructure representation of join alias variables. An explicit JOIN

now has an RTE of its own, and references to its outputs now are Vars
referencing the JOIN RTE, rather than CASE-expressions.  This allows
reverse-listing in ruleutils.c to use the correct alias easily, rather
than painfully reverse-engineering the alias namespace as it used to do.
Also, nested FULL JOINs work correctly, because the result of the inner
joins are simple Vars that the planner can cope with.  This fixes a bug
reported a couple times now, notably by Tatsuo on 18-Nov-01.  The alias
Vars are expanded into COALESCE expressions where needed at the very end
of planning, rather than during parsing.
Also, beginnings of support for showing plan qualifier expressions in
EXPLAIN.  There are probably still cases that need work.
initdb forced due to change of stored-rule representation.

src/include/parser/parsetree.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsetree.h,v 1.16 2001/11/05 17:46:35 momjian Exp $
+ * $Id: parsetree.h,v 1.17 2002/03/12 00:52:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,7 +41,7 @@
  *
  *		Given the range index of a relation, return the corresponding
  *		relation OID.  Note that InvalidOid will be returned if the
- *		RTE is for a sub-select rather than a relation.
+ *		RTE is for a non-relation-type RTE.
  */
 #define getrelid(rangeindex,rangetable) \
 	(rt_fetch(rangeindex, rangetable)->relid)
@@ -52,4 +52,11 @@
  */
 extern char *get_rte_attribute_name(RangeTblEntry *rte, AttrNumber attnum);
 
+/*
+ * Given an RTE and an attribute number, return the appropriate
+ * type and typemod info for that attribute of that RTE.
+ */
+extern void get_rte_attribute_type(RangeTblEntry *rte, AttrNumber attnum,
+								   Oid *vartype, int32 *vartypmod);
+
 #endif   /* PARSETREE_H */