Reimplementation of UNION/INTERSECT/EXCEPT. INTERSECT/EXCEPT now meet the

SQL92 semantics, including support for ALL option.  All three can be used
in subqueries and views.  DISTINCT and ORDER BY work now in views, too.
This rewrite fixes many problems with cross-datatype UNIONs and INSERT/SELECT
where the SELECT yields different datatypes than the INSERT needs.  I did
that by making UNION subqueries and SELECT in INSERT be treated like
subselects-in-FROM, thereby allowing an extra level of targetlist where the
datatype conversions can be inserted safely.
INITDB NEEDED!

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.76 2000/09/29 18:21:23 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.77 2000/10/05 19:11:32 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1636,8 +1636,8 @@ simplify_op_or_func(Expr *expr, List *args)
  * so that a scan of a target list can be handled without additional code.
  * (But only the "expr" part of a TargetEntry is examined, unless the walker
  * chooses to process TargetEntry nodes specially.)  Also, RangeTblRef,
- * FromExpr, and JoinExpr nodes are handled, so that qual expressions in a
- * jointree can be processed without additional code.
+ * FromExpr, JoinExpr, and SetOperationStmt nodes are handled, so that query
+ * jointrees and setOperation trees can be processed without additional code.
  *
  * expression_tree_walker will handle SubLink and SubPlan nodes by recursing
  * normally into the "lefthand" arguments (which belong to the outer plan).
@@ -1654,7 +1654,8 @@ simplify_op_or_func(Expr *expr, List *args)
  *		if (IsA(node, Query))
  *		{
  *			adjust context for subquery;
- *			result = query_tree_walker((Query *) node, my_walker, context);
+ *			result = query_tree_walker((Query *) node, my_walker, context,
+ *									   true); // to visit subquery RTEs too
  *			restore context if needed;
  *			return result;
  *		}
@@ -1827,6 +1828,16 @@ expression_tree_walker(Node *node,
 				 */
 			}
 			break;
+		case T_SetOperationStmt:
+			{
+				SetOperationStmt *setop = (SetOperationStmt *) node;
+
+				if (walker(setop->larg, context))
+					return true;
+				if (walker(setop->rarg, context))
+					return true;
+			}
+			break;
 		default:
 			elog(ERROR, "expression_tree_walker: Unexpected node type %d",
 				 nodeTag(node));
@@ -1843,11 +1854,17 @@ expression_tree_walker(Node *node,
  * for starting a walk at top level of a Query regardless of whether the
  * walker intends to descend into subqueries.  It is also useful for
  * descending into subqueries within a walker.
+ *
+ * If visitQueryRTEs is true, the walker will also be called on sub-Query
+ * nodes present in subquery rangetable entries of the given Query.  This
+ * is optional since some callers handle those sub-queries separately,
+ * or don't really want to see subqueries anyway.
  */
 bool
 query_tree_walker(Query *query,
 				  bool (*walker) (),
-				  void *context)
+				  void *context,
+				  bool visitQueryRTEs)
 {
 	Assert(query != NULL && IsA(query, Query));
 
@@ -1855,11 +1872,23 @@ query_tree_walker(Query *query,
 		return true;
 	if (walker((Node *) query->jointree, context))
 		return true;
+	if (walker(query->setOperations, context))
+		return true;
 	if (walker(query->havingQual, context))
 		return true;
-	/*
-	 * XXX for subselect-in-FROM, may need to examine rtable as well?
-	 */
+	if (visitQueryRTEs)
+	{
+		List   *rt;
+
+		foreach(rt, query->rtable)
+		{
+			RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
+
+			if (rte->subquery)
+				if (walker(rte->subquery, context))
+					return true;
+		}
+	}
 	return false;
 }
 
@@ -2158,6 +2187,17 @@ expression_tree_mutator(Node *node,
 				return (Node *) newnode;
 			}
 			break;
+		case T_SetOperationStmt:
+			{
+				SetOperationStmt *setop = (SetOperationStmt *) node;
+				SetOperationStmt *newnode;
+
+				FLATCOPY(newnode, setop, SetOperationStmt);
+				MUTATE(newnode->larg, setop->larg, Node *);
+				MUTATE(newnode->rarg, setop->rarg, Node *);
+				return (Node *) newnode;
+			}
+			break;
 		default:
 			elog(ERROR, "expression_tree_mutator: Unexpected node type %d",
 				 nodeTag(node));
@@ -2166,3 +2206,58 @@ expression_tree_mutator(Node *node,
 	/* can't get here, but keep compiler happy */
 	return NULL;
 }
+
+
+/*
+ * query_tree_mutator --- initiate modification of a Query's expressions
+ *
+ * This routine exists just to reduce the number of places that need to know
+ * where all the expression subtrees of a Query are.  Note it can be used
+ * for starting a walk at top level of a Query regardless of whether the
+ * mutator intends to descend into subqueries.  It is also useful for
+ * descending into subqueries within a mutator.
+ *
+ * The specified Query node is modified-in-place; do a FLATCOPY() beforehand
+ * if you don't want to change the original.  All substructure is safely
+ * copied, however.
+ *
+ * If visitQueryRTEs is true, the mutator will also be called on sub-Query
+ * nodes present in subquery rangetable entries of the given Query.  This
+ * is optional since some callers handle those sub-queries separately,
+ * or don't really want to see subqueries anyway.
+ */
+void
+query_tree_mutator(Query *query,
+				   Node *(*mutator) (),
+				   void *context,
+				   bool visitQueryRTEs)
+{
+	Assert(query != NULL && IsA(query, Query));
+
+	MUTATE(query->targetList, query->targetList, List *);
+	MUTATE(query->jointree, query->jointree, FromExpr *);
+	MUTATE(query->setOperations, query->setOperations, Node *);
+	MUTATE(query->havingQual, query->havingQual, Node *);
+	if (visitQueryRTEs)
+	{
+		List   *newrt = NIL;
+		List   *rt;
+
+		foreach(rt, query->rtable)
+		{
+			RangeTblEntry *rte = (RangeTblEntry *) lfirst(rt);
+
+			if (rte->subquery)
+			{
+				RangeTblEntry *newrte;
+
+				FLATCOPY(newrte, rte, RangeTblEntry);
+				CHECKFLATCOPY(newrte->subquery, rte->subquery, Query);
+				MUTATE(newrte->subquery, newrte->subquery, Query *);
+				rte = newrte;
+			}
+			newrt = lappend(newrt, rte);
+		}
+		query->rtable = newrt;
+	}
+}