thd pointer fixed

.bzrignore

@@ -919,3 +919,4 @@ vio/test-ssl
 vio/test-sslclient
 vio/test-sslserver
 vio/viotest-ssl
+libmysqld/sql_trigger.cc

mysql-test/r/merge.result

@@ -650,4 +650,6 @@ create table t3 engine=merge union=(t1, t2) select * from t1;
 ERROR HY000: You can't specify target table 't1' for update in FROM clause
 create table t3 engine=merge union=(t1, t2) select * from t2;
 ERROR HY000: You can't specify target table 't2' for update in FROM clause
+create table t3 engine=merge union=(t1, t2) select (select max(a) from t2);
+ERROR HY000: You can't specify target table 't2' for update in FROM clause
 drop table t1, t2;

sql/item_subselect.cc

@@ -272,7 +272,8 @@ Item_singlerow_subselect::Item_singlerow_subselect(st_select_lex *select_lex)
   DBUG_VOID_RETURN;
 }
 
-Item_maxmin_subselect::Item_maxmin_subselect(Item_subselect *parent,
+Item_maxmin_subselect::Item_maxmin_subselect(THD *thd_param,
+                                             Item_subselect *parent,
 					     st_select_lex *select_lex,
 					     bool max_arg)
   :Item_singlerow_subselect()
@@ -291,6 +292,12 @@ Item_maxmin_subselect::Item_maxmin_subselect(Item_subselect *parent,
   used_tables_cache= parent->get_used_tables_cache();
   const_item_cache= parent->get_const_item_cache();
 
+  /*
+    this subquery alwais creates during preparation, so we can assign
+    thd here
+  */
+  thd= thd_param;
+
   DBUG_VOID_RETURN;
 }
 
@@ -316,6 +323,8 @@ Item_singlerow_subselect::select_transformer(JOIN *join)
   SELECT_LEX *select_lex= join->select_lex;
 
   /* Juggle with current arena only if we're in prepared statement prepare */
+  DBUG_PRINT("TANSF:", ("thd %p, select_lex->join->thd: %s",
+                        thd, select_lex->join->thd));
   Item_arena *arena= thd->current_arena;
   Item_arena backup;
   if (arena->is_conventional())
@@ -723,7 +732,7 @@ Item_in_subselect::single_value_transformer(JOIN *join,
       // remove LIMIT placed  by ALL/ANY subquery
       select_lex->master_unit()->global_parameters->select_limit=
 	HA_POS_ERROR;
-      subs= new Item_maxmin_subselect(this, select_lex, func->l_op());
+      subs= new Item_maxmin_subselect(thd, this, select_lex, func->l_op());
     }
     // left expression belong to outer select
     SELECT_LEX *current= thd->lex->current_select, *up;
@@ -899,7 +908,7 @@ Item_in_subselect::row_value_transformer(JOIN *join)
   }
   thd->where= "row IN/ALL/ANY subquery";
 
-  Item_arena *arena= join->thd->current_arena, backup;
+  Item_arena *arena= thd->current_arena, backup;
   if (arena->is_conventional())
     arena= 0;
   else

sql/item_subselect.h

@@ -154,7 +154,7 @@ class Item_maxmin_subselect :public Item_singlerow_subselect
 {
   bool max;
 public:
-  Item_maxmin_subselect(Item_subselect *parent,
+  Item_maxmin_subselect(THD *thd, Item_subselect *parent,
 			st_select_lex *select_lex, bool max);
   void print(String *str);
 };