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mariadb/mysql-test/r/explain.result
unknown 941018f8d1 Patch for mdev-287: CHEAP SQ: A query with subquery in SELECT list, EXISTS, inner joins takes hundreds times longer 
Analysis:

The fix for lp:944706 introduces early subquery optimization.
While a subquery is being optimized some of its predicates may be
removed. In the test case, the EXISTS subquery is constant, and is
evaluated to TRUE. As a result the whole OR is TRUE, and thus the
correlated condition "b = alias1.b" is optimized away. The subquery
becomes non-correlated.

The subquery cache is designed to work only for correlated subqueries.
If constant subquery optimization is disallowed, then the constant
subquery is not evaluated, the subquery remains correlated, and its
execution is cached. As a result execution is fast.

However, when the constant subquery was optimized away, it was neither
cached by the subquery cache, nor it was cached by the internal subquery
caching. The latter was due to the fact that the subquery still appeared
as correlated to the subselect_XYZ_engine::exec methods, and they
re-executed the subquery on each call to Item_subselect::exec.

Solution:

The solution is to update the correlated status of the subquery after it has
been optimized. This status consists of:
- st_select_lex::is_correlated
- Item_subselect::is_correlated
- SELECT_LEX::uncacheable
- SELECT_LEX_UNIT::uncacheable
The status is updated by st_select_lex::update_correlated_cache(), and its
caller st_select_lex::optimize_unflattened_subqueries. The solution relies
on the fact that the optimizer already called
st_select_lex::update_used_tables() for each subquery. This allows to
efficiently update the correlated status of each subquery without walking
the whole subquery tree.

Notice that his patch is an improvement over MySQL 5.6 and older, where
subqueries are not pre-optimized, and the above analysis is not possible.
2012-05-30 00:18:53 +03:00

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drop table if exists t1;
create table t1 (id int not null, str char(10), unique(str));
explain select * from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system NULL NULL NULL NULL 0 const row not found
insert into t1 values (1, null),(2, null),(3, "foo"),(4, "bar");
select * from t1 where str is null;
id str
1 NULL
2 NULL
select * from t1 where str="foo";
id str
3 foo
explain select * from t1 where str is null;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref str str 11 const 1 Using index condition
explain select * from t1 where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const str str 11 const 1
explain select * from t1 ignore key (str) where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using where
explain select * from t1 use key (str,str) where str="foo";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const str str 11 const 1
explain select * from t1 use key (str,str,foo) where str="foo";
ERROR 42000: Key 'foo' doesn't exist in table 't1'
explain select * from t1 ignore key (str,str,foo) where str="foo";
ERROR 42000: Key 'foo' doesn't exist in table 't1'
drop table t1;
explain select 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
create table t1 (a int not null);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
insert into t1 values(1);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
insert into t1 values(1);
explain select count(*) from t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1;
set names koi8r;
create table <20><><EFBFBD> (<28><><EFBFBD>0 int, <20><><EFBFBD>1 int, key <20><><EFBFBD>0 (<28><><EFBFBD>0), key <20><><EFBFBD>01 (<28><><EFBFBD>0,<2C><><EFBFBD>1));
insert into <20><><EFBFBD> (<28><><EFBFBD>0) values (1);
insert into <20><><EFBFBD> (<28><><EFBFBD>0) values (2);
explain select <20><><EFBFBD>0 from <20><><EFBFBD> where <20><><EFBFBD>0=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE <09><><EFBFBD> ref <09><><EFBFBD>0,<2C><><EFBFBD>01 <09><><EFBFBD>0 5 const 1 Using index
drop table <20><><EFBFBD>;
set names latin1;
select 3 into @v1;
explain select 3 into @v1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used
create table t1(f1 int, f2 int);
insert into t1 values (1,1);
create view v1 as select * from t1 where f1=1;
explain extended select * from v1 where f2=1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select 1 AS `f1`,1 AS `f2` from dual where 1
explain extended select * from t1 where 0;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 0
explain extended select * from t1 where 1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select 1 AS `f1`,1 AS `f2` from dual where 1
explain extended select * from t1 having 0;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible HAVING
Warnings:
Note 1003 select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` having 0
explain extended select * from t1 having 1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select 1 AS `f1`,1 AS `f2` from dual having 1
drop view v1;
drop table t1;
CREATE TABLE t1(c INT);
INSERT INTO t1 VALUES (),();
CREATE TABLE t2 (b INT,
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b),
KEY(b),KEY(b),KEY(b),KEY(b),KEY(b));
INSERT INTO t2 VALUES (),(),();
EXPLAIN SELECT 1 FROM
(SELECT 1 FROM t2,t1 WHERE b < c GROUP BY 1 LIMIT 1) AS d2;
id select_type table type possible_keys key key_len ref rows Extra
X X X X X X X X X
X X X X X X X X X
X X X X X X X X X Range checked for each record (index map: 0xFFFFFFFFFF)
DROP TABLE t2;
DROP TABLE t1;
CREATE TABLE t1(a INT);
CREATE TABLE t2(a INT);
INSERT INTO t1 VALUES (1),(2);
INSERT INTO t2 VALUES (1),(2);
EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
prepare s1 from
'EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
prepare s1 from
'EXPLAIN EXTENDED SELECT 1
FROM (SELECT COUNT(DISTINCT t1.a) FROM t1,t2 GROUP BY t1.a) AS s1';
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
execute s1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4 100.00
2 DERIVED t1 ALL NULL NULL NULL NULL 2 100.00 Using temporary; Using filesort
2 DERIVED t2 ALL NULL NULL NULL NULL 2 100.00 Using join buffer (flat, BNL join)
Warnings:
Note 1003 select 1 AS `1` from (select count(distinct `test`.`t1`.`a`) AS `COUNT(DISTINCT t1.a)` from `test`.`t1` join `test`.`t2` group by `test`.`t1`.`a`) `s1`
DROP TABLE t1,t2;
CREATE TABLE t1 (a INT PRIMARY KEY);
EXPLAIN EXTENDED SELECT COUNT(a) FROM t1 USE KEY(a);
ERROR 42000: Key 'a' doesn't exist in table 't1'
DROP TABLE t1;
CREATE TABLE t1(a LONGTEXT);
INSERT INTO t1 VALUES (repeat('a',@@global.max_allowed_packet));
INSERT INTO t1 VALUES (repeat('b',@@global.max_allowed_packet));
EXPLAIN SELECT DISTINCT 1 FROM t1,
(SELECT DISTINCTROW a AS away FROM t1 GROUP BY a WITH ROLLUP) as d1
WHERE t1.a = d1.a;
ERROR 42S22: Unknown column 'd1.a' in 'where clause'
DROP TABLE t1;
#
# Bug#48295:
# explain extended crash with subquery and ONLY_FULL_GROUP_BY sql_mode
#
CREATE TABLE t1 (f1 INT not null);
SELECT @@session.sql_mode INTO @old_sql_mode;
SET SESSION sql_mode='ONLY_FULL_GROUP_BY';
EXPLAIN EXTENDED SELECT 1 FROM t1
WHERE f1 > ALL( SELECT t.f1 FROM t1,t1 AS t );
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
2 SUBQUERY t1 system NULL NULL NULL NULL 0 0.00 const row not found
2 SUBQUERY t system NULL NULL NULL NULL 0 0.00 const row not found
Warnings:
Note 1003 select 1 AS `1` from `test`.`t1` where 0
SET SESSION sql_mode=@old_sql_mode;
DROP TABLE t1;
End of 5.0 tests.
#
# Bug#37870: Usage of uninitialized value caused failed assertion.
#
create table t1 (dt datetime not null, t time not null);
create table t2 (dt datetime not null);
insert into t1 values ('2001-01-01 1:1:1', '1:1:1'),
('2001-01-01 1:1:1', '1:1:1');
insert into t2 values ('2001-01-01 1:1:1'), ('2001-01-01 1:1:1');
SET @save_join_cache_level=@@join_cache_level;
SET join_cache_level=0;
flush tables;
EXPLAIN SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN (SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.dt IS NULL );
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY OUTR ALL NULL NULL NULL NULL 2 Using where
1 PRIMARY INNR ALL NULL NULL NULL NULL 2 Using where; FirstMatch(OUTR)
flush tables;
SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN (SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.dt IS NULL );
dt
flush tables;
EXPLAIN SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN ( SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.t < '2005-11-13 7:41:31' );
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY OUTR ALL NULL NULL NULL NULL 2 Using where
1 PRIMARY INNR ALL NULL NULL NULL NULL 2 Using where; FirstMatch(OUTR)
flush tables;
SELECT OUTR.dt FROM t1 AS OUTR WHERE OUTR.dt IN ( SELECT INNR.dt FROM t2 AS INNR WHERE OUTR.t < '2005-11-13 7:41:31' );
dt
2001-01-01 01:01:01
2001-01-01 01:01:01
SET join_cache_level=@save_join_cache_level;
drop tables t1, t2;
#
# Bug#47669: Query showed by EXPLAIN EXTENDED gives different result from original query
#
CREATE TABLE t1 (c int);
INSERT INTO t1 VALUES (NULL);
CREATE TABLE t2 (d int);
INSERT INTO t2 VALUES (NULL), (0);
EXPLAIN EXTENDED SELECT (SELECT 1 FROM t2 WHERE d = c) FROM t1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1 100.00
2 SUBQUERY t2 ALL NULL NULL NULL NULL 2 100.00 Using where
Warnings:
Note 1276 Field or reference 'test.t1.c' of SELECT #2 was resolved in SELECT #1
Note 1003 select (select 1 from `test`.`t2` where (`test`.`t2`.`d` = NULL)) AS `(SELECT 1 FROM t2 WHERE d = c)` from dual
DROP TABLE t1, t2;
#
# Bug#30302: Tables that were optimized away are printed in the
# EXPLAIN EXTENDED warning.
#
create table t1(f1 int);
create table t2(f2 int);
insert into t1 values(1);
insert into t2 values(1),(2);
explain extended select * from t1 where f1=1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
Warnings:
Note 1003 select 1 AS `f1` from dual where 1
explain extended select * from t1 join t2 on f1=f2 where f1=1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 system NULL NULL NULL NULL 1 100.00
1 SIMPLE t2 ALL NULL NULL NULL NULL 2 100.00 Using where
Warnings:
Note 1003 select 1 AS `f1`,`test`.`t2`.`f2` AS `f2` from `test`.`t2` where (`test`.`t2`.`f2` = 1)
drop table t1,t2;
#
# Bug #48419: another explain crash..
#
CREATE TABLE t1 (a INT);
CREATE TABLE t2 (b BLOB, KEY b(b(100)));
INSERT INTO t2 VALUES ('1'), ('2'), ('3');
FLUSH TABLES;
EXPLAIN SELECT 1 FROM t1 WHERE a = (SELECT 1 FROM t1 t JOIN t2 WHERE b <= 1 AND t.a);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL no matching row in const table
DROP TABLE t1, t2;
#
# Bug #48573: difference of index selection between rpm binary and
# .tar.gz, windows vs linux..
#
CREATE TABLE t1(c1 INT, c2 INT, c4 INT, c5 INT, KEY(c2, c5), KEY(c2, c4, c5));
INSERT INTO t1 VALUES(4, 1, 1, 1);
INSERT INTO t1 VALUES(3, 1, 1, 1);
INSERT INTO t1 VALUES(2, 1, 1, 1);
INSERT INTO t1 VALUES(1, 1, 1, 1);
EXPLAIN SELECT c1 FROM t1 WHERE c2 = 1 AND c4 = 1 AND c5 = 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref c2,c2_2 c2 10 const,const 3 Using where
DROP TABLE t1;
#
# Bug#56814 Explain + subselect + fulltext crashes server
#
CREATE TABLE t1(f1 VARCHAR(6) NOT NULL,
FULLTEXT KEY(f1),UNIQUE(f1));
INSERT INTO t1 VALUES ('test');
EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT t1.f1 FROM t1 JOIN t1 a ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1));
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1
2 SUBQUERY t1 fulltext f1_2,f1 f1 0 1
PREPARE stmt FROM
'EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT t1.f1 FROM t1 RIGHT OUTER JOIN t1 a
ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1))';
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1
2 SUBQUERY t1 fulltext f1_2,f1 f1 0 1
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1
2 SUBQUERY t1 fulltext f1_2,f1 f1 0 1
DEALLOCATE PREPARE stmt;
PREPARE stmt FROM
'EXPLAIN SELECT 1 FROM t1
WHERE 1 > ALL((SELECT t1.f1 FROM t1 JOIN t1 a
ON (MATCH(t1.f1) AGAINST (""))
WHERE t1.f1 GROUP BY t1.f1))';
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1
2 SUBQUERY t1 fulltext f1_2,f1 f1 0 1
EXECUTE stmt;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 system NULL NULL NULL NULL 1
2 SUBQUERY a system NULL NULL NULL NULL 1
2 SUBQUERY t1 fulltext f1_2,f1 f1 0 1
DEALLOCATE PREPARE stmt;
DROP TABLE t1;
End of 5.1 tests.
#
# Bug#11829785 EXPLAIN EXTENDED CRASH WITH RIGHT OUTER JOIN, SUBQUERIES
#
CREATE TABLE t1(a INT);
INSERT INTO t1 VALUES (0), (0);
PREPARE s FROM
'EXPLAIN EXTENDED
SELECT SUBSTRING(1, (SELECT 1 FROM t1 a1 RIGHT OUTER JOIN t1 ON 0)) AS d
FROM t1 WHERE 0 > ANY (SELECT @a FROM t1)';
EXECUTE s;
ERROR 21000: Subquery returns more than 1 row
DEALLOCATE PREPARE s;
DROP TABLE t1;
#
# Bug#776295: EXPLAIN EXTENDED with always false multiple equality
# in the WHERE condition of a derived table
#
CREATE TABLE t1 (a int) ;
CREATE TABLE t2 (a int) ;
INSERT INTO t2 VALUES (8);
set @tmp_optimizer_switch=@@optimizer_switch;
set optimizer_switch='derived_merge=off,derived_with_keys=off';
EXPLAIN EXTENDED
SELECT * FROM ( SELECT t1.a FROM t1,t2 WHERE t2.a = t1.a ) AS t;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY <derived2> system NULL NULL NULL NULL 0 0.00 const row not found
2 DERIVED NULL NULL NULL NULL NULL NULL NULL NULL no matching row in const table
Warnings:
Note 1003 select NULL AS `a` from (select NULL AS `a` from `test`.`t1` where 0) `t`
set optimizer_switch=@tmp_optimizer_switch;
DROP TABLE t1,t2;
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