added mem_root switching for subselect if it is necessary

(bug #518 fixed)


mysql-test/r/subselect.result:
  test of bug #518
mysql-test/t/subselect.test:
  test of bug #518
sql/item_subselect.cc:
  test and switch mem_root if it is necessary
  exec() - wrapper around engine->exec() to test and switch mem_root if necessary
sql/item_subselect.h:
  added storing THD for mem_root testinmg & switching
  exec() - wrapper around engine->exec() to test and switch mem_root if necessary

mysql-test/r/subselect.result

@@ -1134,3 +1134,17 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ref	salary	salary	5	const	1	Using where
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 drop table t1;
+CREATE TABLE t1 (
+ID int(10) unsigned NOT NULL auto_increment,
+SUB_ID int(3) unsigned NOT NULL default '0',
+REF_ID int(10) unsigned default NULL,
+REF_SUB int(3) unsigned default '0',
+PRIMARY KEY (ID,SUB_ID),
+UNIQUE KEY t1_PK (ID,SUB_ID),
+KEY t1_FK (REF_ID,REF_SUB),
+KEY t1_REFID (REF_ID)
+) TYPE=MyISAM CHARSET=cp1251;
+INSERT INTO t1 VALUES (1,0,NULL,NULL),(2,0,NULL,NULL);
+SELECT DISTINCT REF_ID FROM t1 WHERE ID= (SELECT DISTINCT REF_ID FROM t1 WHERE ID=2);
+REF_ID
+DROP TABLE t1;

mysql-test/t/subselect.test

@@ -716,3 +716,17 @@ create table t1 (id int not null auto_increment primary key, salary int, key(sal
 insert into t1 (salary) values (100),(1000),(10000),(10),(500),(5000),(50000);
 explain SELECT id FROM t1 where salary = (SELECT MAX(salary) FROM t1);
 drop table t1;
+
+CREATE TABLE t1 (
+  ID int(10) unsigned NOT NULL auto_increment,
+  SUB_ID int(3) unsigned NOT NULL default '0',
+  REF_ID int(10) unsigned default NULL,
+  REF_SUB int(3) unsigned default '0',
+  PRIMARY KEY (ID,SUB_ID),
+  UNIQUE KEY t1_PK (ID,SUB_ID),
+  KEY t1_FK (REF_ID,REF_SUB),
+  KEY t1_REFID (REF_ID)
+) TYPE=MyISAM CHARSET=cp1251;
+INSERT INTO t1 VALUES (1,0,NULL,NULL),(2,0,NULL,NULL);
+SELECT DISTINCT REF_ID FROM t1 WHERE ID= (SELECT DISTINCT REF_ID FROM t1 WHERE ID=2);
+DROP TABLE t1;

sql/item_subselect.cc

@@ -79,8 +79,10 @@ void Item_subselect::select_transformer(THD *thd, st_select_lex_unit *unit)
 }
 
 
-bool Item_subselect::fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
+bool Item_subselect::fix_fields(THD *thd_param, TABLE_LIST *tables, Item **ref)
 {
+  thd= thd_param;
+
   if (substitution)
   {
     (*ref)= substitution;
@@ -115,6 +117,20 @@ bool Item_subselect::fix_fields(THD *thd, TABLE_LIST *tables, Item **ref)
   return res;
 }
 
+bool Item_subselect::exec()
+{
+  MEM_ROOT *old_root= my_pthread_getspecific_ptr(MEM_ROOT*, THR_MALLOC);
+  if (&thd->mem_root != old_root)
+  {
+    my_pthread_setspecific_ptr(THR_MALLOC, &thd->mem_root);
+    int res= engine->exec();
+    my_pthread_setspecific_ptr(THR_MALLOC, old_root);
+    return (res);
+  }
+  else
+    return engine->exec();
+}
+
 Item::Type Item_subselect::type() const 
 {
   return SUBSELECT_ITEM;
@@ -253,12 +269,12 @@ bool Item_singlerow_subselect::null_inside()
 
 void Item_singlerow_subselect::bring_value()
 {
-  engine->exec();
+  exec();
 }
 
 double Item_singlerow_subselect::val () 
 {
-  if (!engine->exec() && !value->null_value)
+  if (!exec() && !value->null_value)
   {
     null_value= 0;
     return value->val();
@@ -272,7 +288,7 @@ double Item_singlerow_subselect::val ()
 
 longlong Item_singlerow_subselect::val_int () 
 {
-  if (!engine->exec() && !value->null_value)
+  if (!exec() && !value->null_value)
   {
     null_value= 0;
     return value->val_int();
@@ -286,7 +302,7 @@ longlong Item_singlerow_subselect::val_int ()
 
 String *Item_singlerow_subselect::val_str (String *str) 
 {
-  if (!engine->exec() && !value->null_value)
+  if (!exec() && !value->null_value)
   {
     null_value= 0;
     return value->val_str(str);
@@ -354,7 +370,7 @@ void Item_exists_subselect::fix_length_and_dec()
 
 double Item_exists_subselect::val () 
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     return 0;
@@ -364,7 +380,7 @@ double Item_exists_subselect::val ()
 
 longlong Item_exists_subselect::val_int () 
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     return 0;
@@ -374,7 +390,7 @@ longlong Item_exists_subselect::val_int ()
 
 String *Item_exists_subselect::val_str(String *str)
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     return 0;
@@ -385,7 +401,7 @@ String *Item_exists_subselect::val_str(String *str)
 
 double Item_in_subselect::val () 
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     null_value= 1;
@@ -398,7 +414,7 @@ double Item_in_subselect::val ()
 
 longlong Item_in_subselect::val_int () 
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     null_value= 1;
@@ -411,7 +427,7 @@ longlong Item_in_subselect::val_int ()
 
 String *Item_in_subselect::val_str(String *str)
 {
-  if (engine->exec())
+  if (exec())
   {
     reset();
     null_value= 1;

sql/item_subselect.h

@@ -36,6 +36,8 @@ class Item_subselect :public Item_result_field
   my_bool engine_owner; /* Is this item owner of engine */
   my_bool value_assigned; /* value already assigned to subselect */
 protected:
+  /* thread handler, will be assigned in fix_fields only */
+  THD *thd;
   /* substitution instead of subselect in case of optimization */
   Item *substitution;
   /* engine that perform execution of subselect (single select or union) */
@@ -81,6 +83,7 @@ public:
     return null_value;
   }
   bool fix_fields(THD *thd, TABLE_LIST *tables, Item **ref);
+  bool exec();
   virtual void fix_length_and_dec();
   table_map used_tables() const;