Commit 13515c01 authored by unknown's avatar unknown
Browse files

Merge mysql.com:/home/gluh/MySQL/Merge/4.1 

into  mysql.com:/home/gluh/MySQL/Merge/4.1-opt
parents 8ca9c928 33446269

mysql-test/r/subselect.result

+13 −0
Original line number Diff line number Diff line
@@ -3013,3 +3013,16 @@ t3 CREATE TABLE `t3` ( 
  `a` datetime default NULL

) ENGINE=MyISAM DEFAULT CHARSET=latin1

DROP TABLE t1,t2,t3;

CREATE TABLE t1 (a int);

INSERT INTO t1 VALUES (1), (2);

SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) > 0;

a

SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) IS NULL;

a

1

2

EXPLAIN SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) IS NULL;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	

2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE

DROP TABLE t1;

mysql-test/t/subselect.test

+12 −0
Original line number Diff line number Diff line
@@ -1981,4 +1981,16 @@ SHOW CREATE TABLE t3; 


DROP TABLE t1,t2,t3;



#

# Bug 24670: subquery witout tables but with a WHERE clause

#



CREATE TABLE t1 (a int);

INSERT INTO t1 VALUES (1), (2);



SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) > 0;

SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) IS NULL;

EXPLAIN SELECT a FROM t1 WHERE (SELECT 1 FROM DUAL WHERE 1=0) IS NULL;



DROP TABLE t1;

# End of 4.1 tests

sql/item_subselect.cc

+17 −2
Original line number Diff line number Diff line
@@ -350,6 +350,7 @@ Item_singlerow_subselect::select_transformer(JOIN *join) 
      */

      !(select_lex->item_list.head()->type() == FIELD_ITEM ||

	select_lex->item_list.head()->type() == REF_ITEM) &&

      !join->conds && !join->having &&

      /*

        switch off this optimisation for prepare statement,

        because we do not rollback this changes
@@ -374,8 +375,6 @@ Item_singlerow_subselect::select_transformer(JOIN *join) 
    */

    substitution->walk(&Item::remove_dependence_processor,

		       (byte *) select_lex->outer_select());

    /* SELECT without FROM clause can't have WHERE or HAVING clause */

    DBUG_ASSERT(join->conds == 0 && join->having == 0);

    return RES_REDUCE;

  }

  return RES_OK;
@@ -1795,6 +1794,22 @@ bool subselect_single_select_engine::no_tables() 
}





/*

  Check statically whether the subquery can return NULL



  SINOPSYS

    subselect_single_select_engine::may_be_null()



  RETURN

    FALSE  can guarantee that the subquery never return NULL

    TRUE   otherwise

*/

bool subselect_single_select_engine::may_be_null()

{

  return ((no_tables() && !join->conds && !join->having) ? maybe_null : 1);

}





/*

  Report about presence of tables in subquery

sql/item_subselect.h

+2 −1
Original line number Diff line number Diff line
@@ -301,7 +301,7 @@ class subselect_engine: public Sql_alloc 
  enum Item_result type() { return res_type; }

  enum_field_types field_type() { return res_field_type; }

  virtual void exclude()= 0;

  bool may_be_null() { return maybe_null; };

  virtual bool may_be_null() { return maybe_null; };

  virtual table_map upper_select_const_tables()= 0;

  static table_map calc_const_tables(TABLE_LIST *);

  virtual void print(String *str)= 0;
@@ -335,6 +335,7 @@ class subselect_single_select_engine: public subselect_engine 
  void print (String *str);

  int change_item(Item_subselect *si, select_subselect *result);

  bool no_tables();

  bool may_be_null();

};