fixed error handling if creating derived table failed

single row subquery always can return NULL (no rows found) (BUG#5590)

mysql-test/r/subselect.result

@@ -1084,7 +1084,7 @@ SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
   `a` bigint(20) NOT NULL default '0',
-  `(SELECT a)` bigint(20) NOT NULL default '0'
+  `(SELECT a)` bigint(20) default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
 CREATE TABLE t1 SELECT * FROM (SELECT 1 as a,(SELECT a+0)) a;
@@ -1102,7 +1102,7 @@ a
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` bigint(20) NOT NULL default '0'
+  `a` bigint(20) default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
 create table t1 (a int);
@@ -1976,3 +1976,14 @@ create table t1 (x int);
 select  (select b.x from t1 as b where b.x=a.x) from t1 as a where a.x=2 group by a.x;
 (select b.x from t1 as b where b.x=a.x)
 drop table t1;
+CREATE TABLE `t1` ( `master` int(10) unsigned NOT NULL default '0', `map` smallint(6) unsigned NOT NULL default '0', `slave` int(10) unsigned NOT NULL default '0', `access` int(10) unsigned NOT NULL default '0', UNIQUE KEY `access_u` (`master`,`map`,`slave`));
+INSERT INTO `t1` VALUES (1,0,0,700),(1,1,1,400),(1,5,5,400),(1,12,12,400),(1,12,32,400),(4,12,32,400);
+CREATE TABLE `t2` ( `id` int(10) unsigned NOT NULL default '0', `pid` int(10) unsigned NOT NULL default '0', `map` smallint(6) unsigned NOT NULL default '0', `level` tinyint(4) unsigned NOT NULL default '0', `title` varchar(255) default NULL, PRIMARY KEY  (`id`,`pid`,`map`), KEY `level` (`level`), KEY `id` (`id`,`map`)) ;
+INSERT INTO `t2` VALUES (6,5,12,7,'a'),(12,0,0,7,'a'),(12,1,0,7,'a'),(12,5,5,7,'a'),(12,5,12,7,'a');
+SELECT b.sc FROM (SELECT (SELECT a.access FROM t1 a WHERE a.map = op.map AND a.slave = op.pid AND a.master = 1) ac FROM t2 op WHERE op.id = 12 AND op.map = 0) b;
+ERROR 42S22: Unknown column 'b.sc' in 'field list'
+SELECT b.ac FROM (SELECT (SELECT a.access FROM t1 a WHERE a.map = op.map AND a.slave = op.pid AND a.master = 1) ac FROM t2 op WHERE op.id = 12 AND op.map = 0) b;
+ac
+700
+NULL
+drop tables t1,t2;

mysql-test/t/subselect.test

@@ -1270,3 +1270,16 @@ drop table t1;
 create table t1 (x int);
 select  (select b.x from t1 as b where b.x=a.x) from t1 as a where a.x=2 group by a.x;
 drop table t1;
+
+#
+# Test of correct maybe_null flag returning by subquwery for temporary table
+# creation
+#
+CREATE TABLE `t1` ( `master` int(10) unsigned NOT NULL default '0', `map` smallint(6) unsigned NOT NULL default '0', `slave` int(10) unsigned NOT NULL default '0', `access` int(10) unsigned NOT NULL default '0', UNIQUE KEY `access_u` (`master`,`map`,`slave`));
+INSERT INTO `t1` VALUES (1,0,0,700),(1,1,1,400),(1,5,5,400),(1,12,12,400),(1,12,32,400),(4,12,32,400);
+CREATE TABLE `t2` ( `id` int(10) unsigned NOT NULL default '0', `pid` int(10) unsigned NOT NULL default '0', `map` smallint(6) unsigned NOT NULL default '0', `level` tinyint(4) unsigned NOT NULL default '0', `title` varchar(255) default NULL, PRIMARY KEY  (`id`,`pid`,`map`), KEY `level` (`level`), KEY `id` (`id`,`map`)) ;
+INSERT INTO `t2` VALUES (6,5,12,7,'a'),(12,0,0,7,'a'),(12,1,0,7,'a'),(12,5,5,7,'a'),(12,5,12,7,'a');
+-- error 1054
+SELECT b.sc FROM (SELECT (SELECT a.access FROM t1 a WHERE a.map = op.map AND a.slave = op.pid AND a.master = 1) ac FROM t2 op WHERE op.id = 12 AND op.map = 0) b;
+SELECT b.ac FROM (SELECT (SELECT a.access FROM t1 a WHERE a.map = op.map AND a.slave = op.pid AND a.master = 1) ac FROM t2 op WHERE op.id = 12 AND op.map = 0) b;
+drop tables t1,t2;

sql/item.cc

@@ -2486,6 +2486,7 @@ Item_type_holder::Item_type_holder(THD *thd, Item *item)
   else
     field_example= 0;
   max_length= real_length(item);
+  maybe_null= item->maybe_null;
   collation.set(item->collation);
 }
 

sql/item_subselect.cc

@@ -401,7 +401,6 @@ void Item_singlerow_subselect::fix_length_and_dec()
     engine->fix_length_and_dec(row);
     value= *row;
   }
-  maybe_null= engine->may_be_null();
 }
 
 uint Item_singlerow_subselect::cols()

sql/sql_derived.cc

@@ -224,7 +224,10 @@ static int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit,
     }
   }
   else
+  {
     free_tmp_table(thd, table);
+    thd->lex->unit.cleanup();
+  }
 
 exit:
   delete derived_result;