fixed bug reported by Walrus & Miguel in exists subselect

mysql-test/r/subselect.result:
  added test suite of EXISTS clause
mysql-test/t/subselect.test:
  added test suite of EXISTS clause
sql/item_subselect.cc:
  added checking out of memory
  fixed bug in exists subselect

mysql-test/r/subselect.result

 select (select 2);
 (select 2)
 2
-drop table if exists t1,t2,t3,t4;
+drop table if exists t1,t2,t3,t4,attend,clinic;
 create table t1 (a int);
 create table t2 (a int, b int);
 create table t3 (a int);
@@ -82,4 +82,13 @@ select b,max(a) as ma from t4 group by b having b >= (select max(t2.a)
 from t2 where t2.b=t4.b);
 b	ma
 7	12
-drop table t1,t2,t3,t4;
+create table attend (patient_uq int, clinic_uq int, index i1 (clinic_uq));
+create table clinic( uq int primary key, name char(25));
+insert into clinic values(1,"Oblastnaia bolnitsa"),(2,"Bolnitsa Krasnogo Kresta");
+insert into attend values (1,1),(1,2),(2,2),(1,3);
+select * from attend where exists (select * from clinic where uq = clinic_uq);
+patient_uq	clinic_uq
+1	1
+1	2
+2	2
+drop table t1,t2,t3,t4,attend,clinic;

mysql-test/t/subselect.test

 
 select (select 2);
-drop table if exists t1,t2,t3,t4;
+drop table if exists t1,t2,t3,t4,attend,clinic;
 create table t1 (a int);
 create table t2 (a int, b int);
 create table t3 (a int);
@@ -33,4 +33,11 @@ select b,max(a) as ma from t4 group by b having b < (select max(t2.a)
 from t2 where t2.b=t4.b);
 select b,max(a) as ma from t4 group by b having b >= (select max(t2.a)
 from t2 where t2.b=t4.b);
-drop table t1,t2,t3,t4;
+
+create table attend (patient_uq int, clinic_uq int, index i1 (clinic_uq));
+create table clinic( uq int primary key, name char(25));
+insert into clinic values(1,"Oblastnaia bolnitsa"),(2,"Bolnitsa Krasnogo Kresta");
+insert into attend values (1,1),(1,2),(2,2),(1,3);
+select * from attend where exists (select * from clinic where uq = clinic_uq);
+
+drop table t1,t2,t3,t4,attend,clinic;

sql/item_subselect.cc

@@ -51,6 +51,12 @@ Item_subselect::Item_subselect(THD *thd, st_select_lex *select_lex,
   if (unit->select_limit_cnt == HA_POS_ERROR)
     select_lex->options&= ~OPTION_FOUND_ROWS;
   join= new JOIN(thd, select_lex->item_list, select_lex->options, result);
+  if (!join || !result)
+  {
+    //out of memory
+    thd->fatal_error= 1;
+    my_printf_error(ER_OUT_OF_RESOURCES, ER(ER_OUT_OF_RESOURCES), MYF(0));
+  } 
   this->select_lex= select_lex;
   assign_null();
   /*
@@ -172,7 +178,7 @@ String *Item_singleval_subselect::val_str (String *str)
 
 Item_exists_subselect::Item_exists_subselect(THD *thd,
 					     st_select_lex *select_lex):
-  Item_subselect(thd, select_lex, new select_singleval_subselect(this))
+  Item_subselect(thd, select_lex, new select_exists_subselect(this))
 {
   max_columns= UINT_MAX;
   null_value= 0; //can't be NULL