From 6bc61fc046961cfc2b3901ab38ac74b45f8c6cd3 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 9 Jan 2003 20:50:53 +0000
Subject: Adjust parser so that 'x NOT IN (subselect)' is converted to 'NOT (x
 IN (subselect))', that is 'NOT (x = ANY (subselect))', rather than 'x <> ALL
 (subselect)' as we formerly did.  This opens the door to optimizing NOT IN
 the same way as IN, whereas there's no hope of optimizing the expression
 using <>.  Also, convert 'x <> ALL (subselect)' to the NOT(IN) style, so that
 the optimization will be available when processing rules dumped by older
 Postgres versions. initdb forced due to small change in SubLink node
 representation.

---
 src/backend/parser/parse_expr.c | 48 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 45 insertions(+), 3 deletions(-)

(limited to 'src/backend/parser/parse_expr.c')

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 9705ca5d7de..3701f41dca0 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_expr.c,v 1.138 2002/12/27 20:06:19 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_expr.c,v 1.139 2003/01/09 20:50:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -367,6 +367,8 @@ transformExpr(ParseState *pstate, Node *expr)
 					 */
 					sublink->lefthand = NIL;
 					sublink->oper = NIL;
+					sublink->operIsEquals = FALSE;
+					sublink->useOr = FALSE;
 				}
 				else if (sublink->subLinkType == EXPR_SUBLINK)
 				{
@@ -391,27 +393,60 @@ transformExpr(ParseState *pstate, Node *expr)
 					 */
 					sublink->lefthand = NIL;
 					sublink->oper = NIL;
+					sublink->operIsEquals = FALSE;
+					sublink->useOr = FALSE;
 				}
 				else
 				{
 					/* ALL, ANY, or MULTIEXPR: generate operator list */
 					List	   *left_list = sublink->lefthand;
 					List	   *right_list = qtree->targetList;
+					int			row_length = length(left_list);
+					bool		needNot = false;
 					List	   *op;
 					char	   *opname;
 					List	   *elist;
 
+					/* transform lefthand expressions */
 					foreach(elist, left_list)
 						lfirst(elist) = transformExpr(pstate, lfirst(elist));
 
+					/* get the combining-operator name */
 					Assert(IsA(sublink->oper, A_Expr));
 					op = ((A_Expr *) sublink->oper)->name;
 					opname = strVal(llast(op));
 					sublink->oper = NIL;
 
+					/*
+					 * If the expression is "<> ALL" (with unqualified opname)
+					 * then convert it to "NOT IN".  This is a hack to improve
+					 * efficiency of expressions output by pre-7.4 Postgres.
+					 */
+					if (sublink->subLinkType == ALL_SUBLINK &&
+						length(op) == 1 && strcmp(opname, "<>") == 0)
+					{
+						sublink->subLinkType = ANY_SUBLINK;
+						opname = pstrdup("=");
+						op = makeList1(makeString(opname));
+						needNot = true;
+					}
+
+					/* Set operIsEquals if op is unqualified "=" */
+					if (length(op) == 1 && strcmp(opname, "=") == 0)
+						sublink->operIsEquals = TRUE;
+					else
+						sublink->operIsEquals = FALSE;
+
+					/* Set useOr if op is "<>" (possibly qualified) */
+					if (strcmp(opname, "<>") == 0)
+						sublink->useOr = TRUE;
+					else
+						sublink->useOr = FALSE;
+
 					/* Combining operators other than =/<> is dubious... */
-					if (length(left_list) != 1 &&
-					strcmp(opname, "=") != 0 && strcmp(opname, "<>") != 0)
+					if (row_length != 1 &&
+						strcmp(opname, "=") != 0 &&
+						strcmp(opname, "<>") != 0)
 						elog(ERROR, "Row comparison cannot use operator %s",
 							 opname);
 
@@ -474,6 +509,13 @@ transformExpr(ParseState *pstate, Node *expr)
 					}
 					if (left_list != NIL)
 						elog(ERROR, "Subselect has too few fields");
+
+					if (needNot)
+					{
+						expr = coerce_to_boolean(expr, "NOT");
+						expr = (Node *) makeBoolExpr(NOT_EXPR,
+													 makeList1(expr));
+					}
 				}
 				result = (Node *) expr;
 				break;
-- 
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