EXISTS(SELECT * ...)

close table before opening in optimize


mysql-test/r/subselect.result:
  test of EXISTS(SELECT * ...)
mysql-test/t/subselect.test:
  test of EXISTS(SELECT * ...)
sql/sql_base.cc:
  EXISTS(SELECT * ...)
sql/sql_table.cc:
  close table before opening one

mysql-test/r/subselect.result

@@ -328,10 +328,10 @@ patient_uq	clinic_uq
 explain extended select * from t6 where exists (select * from t7 where uq = clinic_uq);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t6	ALL	NULL	NULL	NULL	NULL	4	Using where
-2	DEPENDENT SUBQUERY	t7	eq_ref	PRIMARY	PRIMARY	4	test.t6.clinic_uq	1	
+2	DEPENDENT SUBQUERY	t7	eq_ref	PRIMARY	PRIMARY	4	test.t6.clinic_uq	1	Using index
 Warnings:
 Note	1276	Field or reference 'clinic_uq' of SELECT #2 was resolved in SELECT #1
-Note	1003	select test.t6.patient_uq AS `patient_uq`,test.t6.clinic_uq AS `clinic_uq` from test.t6 where exists(select test.t7.uq AS `uq`,test.t7.name AS `name` from test.t7 where (test.t7.uq = test.t6.clinic_uq))
+Note	1003	select test.t6.patient_uq AS `patient_uq`,test.t6.clinic_uq AS `clinic_uq` from test.t6 where exists(select 1 AS `Not_used` from test.t7 where (test.t7.uq = test.t6.clinic_uq))
 select * from t1 where a= (select a from t2,t4 where t2.b=t4.b);
 ERROR 23000: Column: 'a' in field list is ambiguous
 drop table t1,t2,t3;
@@ -1817,3 +1817,17 @@ a
 1
 3
 DROP TABLE t1;
+create table t1 (a int, b int);
+insert into t1 values (1,2),(3,4);
+select * from t1 up where exists (select * from t1 where t1.a=up.a);
+a	b
+1	2
+3	4
+explain extended select * from t1 up where exists (select * from t1 where t1.a=up.a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	up	ALL	NULL	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+Warnings:
+Note	1276	Field or reference 'up.a' of SELECT #2 was resolved in SELECT #1
+Note	1003	select test.up.a AS `a`,test.up.b AS `b` from test.t1 up where exists(select 1 AS `Not_used` from test.t1 where (test.t1.a = test.up.a))
+drop table t1;

mysql-test/t/subselect.test

@@ -1158,3 +1158,12 @@ SELECT a FROM t1 WHERE a >= ALL ( SELECT a FROM t1 WHERE b = 2 );
 SELECT a FROM t1 WHERE a <= ALL ( SELECT a FROM t1 WHERE b = 2 );
 SELECT a FROM t1 WHERE a <> ALL ( SELECT a FROM t1 WHERE b = 2 );
 DROP TABLE t1;
+
+#
+# SELECT(EXISTS * ...)optimisation
+#
+create table t1 (a int, b int);
+insert into t1 values (1,2),(3,4);
+select * from t1 up where exists (select * from t1 where t1.a=up.a);
+explain extended select * from t1 up where exists (select * from t1 where t1.a=up.a);
+drop table t1;

sql/sql_base.cc

@@ -2184,7 +2184,18 @@ int setup_wild(THD *thd, TABLE_LIST *tables, List<Item> &fields,
 	!((Item_field*) item)->field)
     {
       uint elem= fields.elements;
-      if (insert_fields(thd,tables,((Item_field*) item)->db_name,
+      Item_subselect *subsel= thd->lex->current_select->master_unit()->item;
+      if (subsel &&
+          subsel->substype() == Item_subselect::EXISTS_SUBS)
+      {
+        /*
+          It is EXISTS(SELECT * ...) and we can replace * by any constant.
+
+          Item_int do not need fix_fields() because it is basic constant.
+        */
+        it.replace(new Item_int("Not_used", (longlong) 1, 21));
+      }
+      else if (insert_fields(thd,tables,((Item_field*) item)->db_name,
                              ((Item_field*) item)->table_name, &it))
       {
 	if (stmt)

sql/sql_table.cc

@@ -1861,6 +1861,7 @@ static int mysql_admin_table(THD* thd, TABLE_LIST* tables,
       TABLE_LIST *save_next= table->next;
       table->next= 0;
       result_code= mysql_recreate_table(thd, table, 0);
+      close_thread_tables(thd);
       if (!result_code) // recreation went ok
       {
         if ((table->table= open_ltable(thd, table, lock_type)) &&