Fix for the optimiser problem caused by the fact that with derived

tables one (or more tables) is opened / closed twice.

mysql-test/r/derived.result

@@ -137,7 +137,7 @@ a	t
 explain select count(*) from t1 as tt1, (select * from t1) as tt2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
-2	DERIVED	tt1	index	NULL	a	4	NULL	10000	Using index
+2	DERIVED	tt1	ALL	NULL	NULL	NULL	NULL	10000	
 drop table t1;
 SELECT * FROM (SELECT (SELECT * FROM (SELECT 1 as a) as a )) as b;
 (SELECT * FROM (SELECT 1 as a) as a )

sql/sql_derived.cc

@@ -219,6 +219,8 @@ int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit,
       /* Add new temporary table to list of open derived tables */
       table->next= thd->derived_tables;
       thd->derived_tables= table;
+      thd->query_id++;
+      query_id++;
     }
 
 exit: