fixed cached constsnt determination (bug #142 related)

mysql-test/r/subselect.result:
  test of constant redecing
mysql-test/t/subselect.test:
  test of constant redecing
sql/item_cmpfunc.cc:
  fixed cached constsnt determination

mysql-test/r/subselect.result

@@ -1049,3 +1049,26 @@ select t2.Continent, t1.Name, t1.Population from t2 LEFT JOIN t1 ON t2.Code = t1
 Continent	Name	Population
 Oceania	Sydney	3276207
 drop table t1, t2;
+CREATE TABLE `t1` (
+`id` mediumint(8) unsigned NOT NULL auto_increment,
+`pseudo` varchar(35) character set latin1 NOT NULL default '',
+PRIMARY KEY  (`id`),
+UNIQUE KEY `pseudo` (`pseudo`),
+) TYPE=MyISAM PACK_KEYS=1 ROW_FORMAT=DYNAMIC;
+INSERT INTO t1 (pseudo) VALUES ('test');
+SELECT 0 IN (SELECT 1 FROM t1 a);
+0 IN (SELECT 1 FROM t1 a)
+0
+EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBSELECT	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+INSERT INTO t1 (pseudo) VALUES ('test1');
+SELECT 0 IN (SELECT 1 FROM t1 a);
+0 IN (SELECT 1 FROM t1 a)
+0
+EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBSELECT	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+drop table t1;

mysql-test/t/subselect.test

@@ -644,3 +644,20 @@ INSERT INTO t2 VALUES ('AZE','Azerbaijan','Asia','Middle East',86600.00,1991,773
 select t2.Continent, t1.Name, t1.Population from t2 LEFT JOIN t1 ON t2.Code = t1.t2  where t1.Population IN (select max(t1.Population) AS Population from t1, t2 where t1.t2 = t2.Code group by Continent); 
 
 drop table t1, t2;
+
+#
+# constants in IN
+#
+CREATE TABLE `t1` (
+  `id` mediumint(8) unsigned NOT NULL auto_increment,
+  `pseudo` varchar(35) character set latin1 NOT NULL default '',
+  PRIMARY KEY  (`id`),
+  UNIQUE KEY `pseudo` (`pseudo`),
+) TYPE=MyISAM PACK_KEYS=1 ROW_FORMAT=DYNAMIC;
+INSERT INTO t1 (pseudo) VALUES ('test');
+SELECT 0 IN (SELECT 1 FROM t1 a);
+EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a);
+INSERT INTO t1 (pseudo) VALUES ('test1');
+SELECT 0 IN (SELECT 1 FROM t1 a);
+EXPLAIN SELECT 0 IN (SELECT 1 FROM t1 a);
+drop table t1;

sql/item_cmpfunc.cc

@@ -298,12 +298,22 @@ bool Item_in_optimizer::fix_fields(THD *thd, struct st_table_list *tables,
     return 1;
   cache->setup(args[0]);
   if (cache->cols() == 1)
-    cache->set_used_tables(RAND_TABLE_BIT);
+  {
+    if (args[0]->used_tables())
+      cache->set_used_tables(RAND_TABLE_BIT);
+    else
+      cache->set_used_tables(0);
+  }
   else
   {
     uint n= cache->cols();
     for (uint i= 0; i < n; i++)
-      ((Item_cache *)cache->el(i))->set_used_tables(RAND_TABLE_BIT);
+    {
+      if (args[0]->el(i)->used_tables())
+	((Item_cache *)cache->el(i))->set_used_tables(RAND_TABLE_BIT);
+      else
+	((Item_cache *)cache->el(i))->set_used_tables(0);
+    }
   }
   if (args[1]->fix_fields(thd, tables, args))
     return 1;