Clumsy but working fix for bug #11973 "SELECT .. INTO var_name; in trigger

cause crash on update".

Let us update "thd" pointer in LEX, all its units and in LEX::result before
executing statement in trigger body, since triggers are associated with TABLE
object and because of this can be used in different threads.

mysql-test/r/trigger.result

@@ -635,3 +635,16 @@ show triggers;
 Trigger	Event	Table	Statement	Timing	Created	sql_mode
 t1_bi	INSERT	t1	 set new.a = '2004-01-00'	BEFORE	#	
 drop table t1;
+create table t1 (id int, data int, username varchar(16));
+insert into t1 (id, data) values (1, 0);
+create trigger t1_whoupdated before update on t1 for each row
+begin
+declare user varchar(32);
+declare i int;
+select user() into user;
+set NEW.username = user;
+select count(*) from ((select 1) union (select 2)) as d1 into i;
+end|
+update t1 set data = 1;
+update t1 set data = 2;
+drop table t1;

mysql-test/t/trigger.test

@@ -642,3 +642,26 @@ show create table t1;
 --replace_column 6 #
 show triggers;
 drop table t1;
+
+# Test for bug #11973 "SELECT .. INTO var_name; in trigger cause
+#                      crash on update"
+create table t1 (id int, data int, username varchar(16));
+insert into t1 (id, data) values (1, 0);
+delimiter |;
+create trigger t1_whoupdated before update on t1 for each row
+begin
+  declare user varchar(32);
+  declare i int;
+  select user() into user;
+  set NEW.username = user;
+  select count(*) from ((select 1) union (select 2)) as d1 into i;
+end|
+delimiter ;|
+update t1 set data = 1;
+
+connect (addconroot, localhost, root,,);
+connection addconroot;
+update t1 set data = 2;
+
+connection default;
+drop table t1;

sql/item_subselect.cc

@@ -1271,6 +1271,14 @@ void Item_allany_subselect::print(String *str)
 }
 
 
+void subselect_engine::set_thd(THD *thd_arg)
+{
+  thd= thd_arg;
+  if (result)
+    result->set_thd(thd_arg);
+}
+
+
 subselect_single_select_engine::
 subselect_single_select_engine(st_select_lex *select,
 			       select_subselect *result,

sql/item_subselect.h

@@ -299,8 +299,11 @@ public:
   virtual ~subselect_engine() {}; // to satisfy compiler
   virtual void cleanup()= 0;
 
-  // set_thd should be called before prepare()
-  void set_thd(THD *thd_arg) { thd= thd_arg; }
+  /*
+    Also sets "thd" for subselect_engine::result.
+    Should be called before prepare().
+  */
+  void set_thd(THD *thd_arg);
   THD * get_thd() { return thd; }
   virtual int prepare()= 0;
   virtual void fix_length_and_dec(Item_cache** row)= 0;

sql/sql_class.h

@@ -1560,6 +1560,7 @@ public:
     statement/stored procedure.
   */
   virtual void cleanup();
+  void set_thd(THD *thd_arg) { thd= thd_arg; }
 };
 
 
@@ -1915,14 +1916,13 @@ class multi_delete :public select_result_interceptor
 {
   TABLE_LIST *delete_tables, *table_being_deleted;
   Unique **tempfiles;
-  THD *thd;
   ha_rows deleted, found;
   uint num_of_tables;
   int error;
   bool do_delete, transactional_tables, normal_tables, delete_while_scanning;
 
 public:
-  multi_delete(THD *thd, TABLE_LIST *dt, uint num_of_tables);
+  multi_delete(TABLE_LIST *dt, uint num_of_tables);
   ~multi_delete();
   int prepare(List<Item> &list, SELECT_LEX_UNIT *u);
   bool send_data(List<Item> &items);
@@ -1938,7 +1938,6 @@ class multi_update :public select_result_interceptor
   TABLE_LIST *all_tables; /* query/update command tables */
   TABLE_LIST *leaves;     /* list of leves of join table tree */
   TABLE_LIST *update_tables, *table_being_updated;
-  THD *thd;
   TABLE **tmp_tables, *main_table, *table_to_update;
   TMP_TABLE_PARAM *tmp_table_param;
   ha_rows updated, found;
@@ -1950,7 +1949,7 @@ class multi_update :public select_result_interceptor
   bool do_update, trans_safe, transactional_tables, ignore;
 
 public:
-  multi_update(THD *thd_arg, TABLE_LIST *ut, TABLE_LIST *leaves_list,
+  multi_update(TABLE_LIST *ut, TABLE_LIST *leaves_list,
 	       List<Item> *fields, List<Item> *values,
 	       enum_duplicates handle_duplicates, bool ignore);
   ~multi_update();

sql/sql_delete.cc

@@ -407,9 +407,8 @@ bool mysql_multi_delete_prepare(THD *thd)
 }
 
 
-multi_delete::multi_delete(THD *thd_arg, TABLE_LIST *dt,
-			   uint num_of_tables_arg)
-  : delete_tables(dt), thd(thd_arg), deleted(0), found(0),
+multi_delete::multi_delete(TABLE_LIST *dt, uint num_of_tables_arg)
+  : delete_tables(dt), deleted(0), found(0),
     num_of_tables(num_of_tables_arg), error(0),
     do_delete(0), transactional_tables(0), normal_tables(0)
 {

sql/sql_lex.h

@@ -458,6 +458,7 @@ public:
   inline bool is_prepared() { return prepared; }
   bool change_result(select_subselect *result, select_subselect *old_result);
   void set_limit(st_select_lex *values);
+  void set_thd(THD *thd_arg) { thd= thd_arg; }
 
   friend void lex_start(THD *thd, uchar *buf, uint length);
   friend int subselect_union_engine::exec();

sql/sql_parse.cc

@@ -3318,7 +3318,7 @@ end_with_restore_list:
     if ((res= mysql_multi_delete_prepare(thd)))
       goto error;
 
-    if (!thd->is_fatal_error && (result= new multi_delete(thd,aux_tables,
+    if (!thd->is_fatal_error && (result= new multi_delete(aux_tables,
 							  lex->table_count)))
     {
       res= mysql_select(thd, &select_lex->ref_pointer_array,

sql/sql_prepare.cc

@@ -1850,6 +1850,13 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
   SELECT_LEX *sl= lex->all_selects_list;
   DBUG_ENTER("reinit_stmt_before_use");
 
+  /*
+    We have to update "thd" pointer in LEX, all its units and in LEX::result,
+    since statements which belong to trigger body are associated with TABLE
+    object and because of this can be used in different threads.
+  */
+  lex->thd= thd;
+
   if (lex->empty_field_list_on_rset)
   {
     lex->empty_field_list_on_rset= 0;
@@ -1888,6 +1895,7 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
       unit->types.empty();
       /* for derived tables & PS (which can't be reset by Item_subquery) */
       unit->reinit_exec_mechanism();
+      unit->set_thd(thd);
     }
   }
 
@@ -1926,7 +1934,10 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
     lex->select_lex.leaf_tables= lex->leaf_tables_insert;
 
   if (lex->result)
+  {
     lex->result->cleanup();
+    lex->result->set_thd(thd);
+  }
 
   DBUG_VOID_RETURN;
 }

sql/sql_update.cc

@@ -820,7 +820,7 @@ bool mysql_multi_update(THD *thd,
   if (mysql_multi_update_prepare(thd))
     DBUG_RETURN(TRUE);
 
-  if (!(result= new multi_update(thd, table_list,
+  if (!(result= new multi_update(table_list,
 				 thd->lex->select_lex.leaf_tables,
 				 fields, values,
 				 handle_duplicates, ignore)))
@@ -846,13 +846,13 @@ bool mysql_multi_update(THD *thd,
 }
 
 
-multi_update::multi_update(THD *thd_arg, TABLE_LIST *table_list,
+multi_update::multi_update(TABLE_LIST *table_list,
 			   TABLE_LIST *leaves_list,
 			   List<Item> *field_list, List<Item> *value_list,
 			   enum enum_duplicates handle_duplicates_arg,
                            bool ignore_arg)
   :all_tables(table_list), leaves(leaves_list), update_tables(0),
-   thd(thd_arg), tmp_tables(0), updated(0), found(0), fields(field_list),
+   tmp_tables(0), updated(0), found(0), fields(field_list),
    values(value_list), table_count(0), copy_field(0),
    handle_duplicates(handle_duplicates_arg), do_update(1), trans_safe(0),
    transactional_tables(1), ignore(ignore_arg)