From 6734182c169a1ecb74dd8495004e896ee4519adb Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 26 Aug 2008 02:16:31 +0000
Subject: [PATCH] Teach eval_const_expressions() to simplify an ArrayCoerceExpr
 to a constant when its input is constant and the element coercion function is
 immutable (or nonexistent, ie, binary-coercible case).  This is an oversight
 in the 8.3 implementation of ArrayCoerceExpr, and its result is that certain
 cases involving IN or NOT IN with constants don't get optimized as they
 should be. Per experimentation with an example from Ow Mun Heng.

---
 src/backend/optimizer/util/clauses.c | 37 +++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index c015be9e9b..55bafa2c96 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.264 2008/08/25 22:42:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.265 2008/08/26 02:16:31 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -2359,6 +2359,41 @@ eval_const_expressions_mutator(Node *node,
 		newexpr->coerceformat = expr->coerceformat;
 		return (Node *) newexpr;
 	}
+	if (IsA(node, ArrayCoerceExpr))
+	{
+		ArrayCoerceExpr *expr = (ArrayCoerceExpr *) node;
+		Expr	   *arg;
+		ArrayCoerceExpr *newexpr;
+
+		/*
+		 * Reduce constants in the ArrayCoerceExpr's argument, then build
+		 * a new ArrayCoerceExpr.
+		 */
+		arg = (Expr *) eval_const_expressions_mutator((Node *) expr->arg,
+													  context);
+
+		newexpr = makeNode(ArrayCoerceExpr);
+		newexpr->arg = arg;
+		newexpr->elemfuncid = expr->elemfuncid;
+		newexpr->resulttype = expr->resulttype;
+		newexpr->resulttypmod = expr->resulttypmod;
+		newexpr->isExplicit = expr->isExplicit;
+		newexpr->coerceformat = expr->coerceformat;
+
+		/*
+		 * If constant argument and it's a binary-coercible or immutable
+		 * conversion, we can simplify it to a constant.
+		 */
+		if (arg && IsA(arg, Const) &&
+			(!OidIsValid(newexpr->elemfuncid) ||
+			 func_volatile(newexpr->elemfuncid) == PROVOLATILE_IMMUTABLE))
+			return (Node *) evaluate_expr((Expr *) newexpr,
+										  newexpr->resulttype,
+										  newexpr->resulttypmod);
+
+		/* Else we must return the partially-simplified node */
+		return (Node *) newexpr;
+	}
 	if (IsA(node, CaseExpr))
 	{
 		/*----------