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941018f8d1
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.
285 lines
12 KiB
Text
285 lines
12 KiB
Text
drop table if exists t1,t2,t3;
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set @exit_optimizer_switch=@@optimizer_switch;
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set optimizer_switch='derived_merge=on,derived_with_keys=on';
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set @save_optimizer_switch=@@optimizer_switch;
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CREATE TABLE t1 (a int not null, b char (10) not null);
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insert into t1 values(1,'a'),(2,'b'),(3,'c'),(3,'c');
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CREATE TABLE t2 (a int not null, b char (10) not null);
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insert into t2 values (3,'c'),(4,'d'),(5,'f'),(6,'e');
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CREATE TABLE t3 (a int not null, b char (10) not null);
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insert into t3 values (3,'f'),(4,'y'),(5,'z'),(6,'c');
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select * from t1 as x1, (select * from t1) as x2;
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a b a b
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1 a 1 a
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2 b 1 a
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3 c 1 a
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3 c 1 a
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1 a 2 b
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2 b 2 b
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3 c 2 b
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3 c 2 b
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1 a 3 c
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2 b 3 c
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3 c 3 c
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3 c 3 c
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1 a 3 c
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2 b 3 c
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3 c 3 c
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3 c 3 c
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explain select * from t1 as x1, (select * from t1) as x2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE x1 ALL NULL NULL NULL NULL 4
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using join buffer (flat, BNL join)
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drop table if exists t2,t3;
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CREATE TABLE t2 (a int not null);
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insert into t2 values(1);
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select * from (select t1.*, t2.a as t2a from t1,t2 where t1.a=t2.a) t1;
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a b t2a
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1 a 1
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explain select * from (select t1.*, t2.a as t2a from t1,t2 where t1.a=t2.a) t1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 system NULL NULL NULL NULL 1
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4 Using where
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drop table t1, t2;
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create table t1(a int not null, t char(8), index(a));
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SELECT * FROM (SELECT * FROM t1) as b ORDER BY a ASC LIMIT 0,20;
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a t
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1 1
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2 2
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3 3
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4 4
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5 5
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6 6
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7 7
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8 8
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9 9
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10 10
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11 11
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12 12
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13 13
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14 14
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15 15
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16 16
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17 17
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18 18
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19 19
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20 20
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explain select count(*) from t1 as tt1, (select * from t1) as tt2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
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drop table t1;
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create table t1 (mat_id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY, matintnum CHAR(6) NOT NULL, test MEDIUMINT UNSIGNED NULL);
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create table t2 (mat_id MEDIUMINT UNSIGNED NOT NULL, pla_id MEDIUMINT UNSIGNED NOT NULL);
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insert into t1 values (NULL, 'a', 1), (NULL, 'b', 2), (NULL, 'c', 3), (NULL, 'd', 4), (NULL, 'e', 5), (NULL, 'f', 6), (NULL, 'g', 7), (NULL, 'h', 8), (NULL, 'i', 9);
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insert into t2 values (1, 100), (1, 101), (1, 102), (2, 100), (2, 103), (2, 104), (3, 101), (3, 102), (3, 105);
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SELECT STRAIGHT_JOIN d.pla_id, m2.mat_id FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum;
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pla_id mat_id
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102 1
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101 1
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100 1
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104 2
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103 2
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105 3
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SELECT STRAIGHT_JOIN d.pla_id, m2.test FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum;
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pla_id test
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102 1
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101 1
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100 1
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104 2
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103 2
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105 3
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explain SELECT STRAIGHT_JOIN d.pla_id, m2.mat_id FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY m2 ALL NULL NULL NULL NULL 9
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1 PRIMARY <derived2> ref key0 key0 7 test.m2.matintnum 2
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2 DERIVED mp ALL NULL NULL NULL NULL 9 Using temporary; Using filesort
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2 DERIVED m1 eq_ref PRIMARY PRIMARY 3 test.mp.mat_id 1
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explain SELECT STRAIGHT_JOIN d.pla_id, m2.test FROM t1 m2 INNER JOIN (SELECT mp.pla_id, MIN(m1.matintnum) AS matintnum FROM t2 mp INNER JOIN t1 m1 ON mp.mat_id=m1.mat_id GROUP BY mp.pla_id) d ON d.matintnum=m2.matintnum;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY m2 ALL NULL NULL NULL NULL 9
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1 PRIMARY <derived2> ref key0 key0 7 test.m2.matintnum 2
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2 DERIVED mp ALL NULL NULL NULL NULL 9 Using temporary; Using filesort
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2 DERIVED m1 eq_ref PRIMARY PRIMARY 3 test.mp.mat_id 1
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drop table t1,t2;
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create table t1 (E1 INTEGER UNSIGNED NOT NULL, E2 INTEGER UNSIGNED NOT NULL, E3 INTEGER UNSIGNED NOT NULL, PRIMARY KEY(E1)
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);
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insert into t1 VALUES(1,1,1), (2,2,1);
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select count(*) from t1 INNER JOIN (SELECT A.E1, A.E2, A.E3 FROM t1 AS A WHERE A.E3 = (SELECT MAX(B.E3) FROM t1 AS B WHERE A.E2 = B.E2)) AS THEMAX ON t1.E1 = THEMAX.E2 AND t1.E1 = t1.E2;
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count(*)
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2
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explain select count(*) from t1 INNER JOIN (SELECT A.E1, A.E2, A.E3 FROM t1 AS A WHERE A.E3 = (SELECT MAX(B.E3) FROM t1 AS B WHERE A.E2 = B.E2)) AS THEMAX ON t1.E1 = THEMAX.E2 AND t1.E1 = t1.E2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE A ALL NULL NULL NULL NULL 2 Using where
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1 SIMPLE t1 eq_ref PRIMARY PRIMARY 4 test.A.E2 1 Using where
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3 DEPENDENT SUBQUERY B ALL NULL NULL NULL NULL 2 Using where
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drop table t1;
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create table t1 (a int);
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insert into t1 values (1),(2);
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select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
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a a
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1 1
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2 1
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1 2
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2 2
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explain select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY <derived2> ALL NULL NULL NULL NULL 4
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1 PRIMARY <derived4> ALL NULL NULL NULL NULL 4 Using join buffer (flat, BNL join)
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4 DERIVED t1 ALL NULL NULL NULL NULL 2
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5 UNION t1 ALL NULL NULL NULL NULL 2
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NULL UNION RESULT <union4,5> ALL NULL NULL NULL NULL NULL
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2 DERIVED t1 ALL NULL NULL NULL NULL 2
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3 UNION t1 ALL NULL NULL NULL NULL 2
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NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
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drop table t1;
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create table t2 (a int, b int, primary key (a));
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insert into t2 values (1,7),(2,7);
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explain select a from t2 where a>1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 index PRIMARY PRIMARY 4 NULL 2 Using where; Using index
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explain select a from (select a from t2 where a>1) tt;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 index PRIMARY PRIMARY 4 NULL 2 Using where; Using index
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drop table t2;
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create table t1
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(
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c1 tinyint, c2 smallint, c3 mediumint, c4 int,
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c5 integer, c6 bigint, c7 float, c8 double,
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c9 double precision, c10 real, c11 decimal(7, 4), c12 numeric(8, 4),
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c13 date, c14 datetime, c15 timestamp, c16 time,
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c17 year, c18 bit, c19 bool, c20 char,
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c21 char(10), c22 varchar(30), c23 tinyblob, c24 tinytext,
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c25 blob, c26 text, c27 mediumblob, c28 mediumtext,
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c29 longblob, c30 longtext, c31 enum('one', 'two', 'three'),
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c32 set('monday', 'tuesday', 'wednesday')
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) engine = MYISAM ;
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create table t2 like t1;
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set @save_optimizer_switch=@@optimizer_switch;
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set @@optimizer_switch="partial_match_rowid_merge=off,partial_match_table_scan=off";
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set @stmt= ' explain SELECT (SELECT SUM(c1 + c12 + 0.0) FROM t2 where (t1.c2 - 0e-3) = t2.c2 GROUP BY t1.c15 LIMIT 1) as scalar_s, exists (select 1.0e+0 from t2 where t2.c3 * 9.0000000000 = t1.c4) as exists_s, c5 * 4 in (select c6 + 0.3e+1 from t2) as in_s, (c7 - 4, c8 - 4) in (select c9 + 4.0, c10 + 40e-1 from t2) as in_row_s FROM t1, (select c25 x, c32 y from t2) tt WHERE x * 1 = c25 ' ;
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prepare stmt1 from @stmt ;
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execute stmt1 ;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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5 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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4 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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3 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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execute stmt1 ;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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5 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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4 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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3 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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explain SELECT (SELECT SUM(c1 + c12 + 0.0) FROM t2 where (t1.c2 - 0e-3) = t2.c2 GROUP BY t1.c15 LIMIT 1) as scalar_s, exists (select 1.0e+0 from t2 where t2.c3 * 9.0000000000 = t1.c4) as exists_s, c5 * 4 in (select c6 + 0.3e+1 from t2) as in_s, (c7 - 4, c8 - 4) in (select c9 + 4.0, c10 + 40e-1 from t2) as in_row_s FROM t1, (select c25 x, c32 y from t2) tt WHERE x * 1 = c25;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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5 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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4 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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3 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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deallocate prepare stmt1;
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drop tables t1,t2;
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set @@optimizer_switch=@save_optimizer_switch;
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#
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# LP bug #793436: query with a derived table for which optimizer proves
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# that it contains not more than 1 row
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#
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CREATE TABLE t1 (a int, KEY (a)) ;
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INSERT INTO t1 VALUES (3), (1);
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CREATE TABLE t2 (a int);
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INSERT INTO t2 VALUES (3);
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EXPLAIN
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SELECT * FROM (SELECT DISTINCT * FROM t2) t, t1 WHERE t1.a = t.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY <derived2> system NULL NULL NULL NULL 1
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1 PRIMARY t1 ref a a 5 const 1 Using index
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2 DERIVED t2 system NULL NULL NULL NULL 1
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SELECT * FROM (SELECT DISTINCT * FROM t2) t, t1 WHERE t1.a = t.a;
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a a
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3 3
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DROP TABLE t1,t2;
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#
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# LP bug #800518: crash with a query over a derived table
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# when a min/max optimization is applied
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#
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CREATE TABLE t1 (a int, b int, c varchar(10), INDEX idx(a,b)) ;
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INSERT INTO t1 VALUES
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(100, 3, 'xxx'), (200, 7, 'yyyyyyy'), (100, 1, 't'),
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(200, 4, 'aaaa'), (100, 3, 'eee'), (100, 5, 'zzzzz');
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EXPLAIN
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SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
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SELECT MAX(b) FROM (SELECT * FROM t1) AS t WHERE a = 100;
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MAX(b)
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5
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DROP TABLE t1;
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#
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# LP bug #799499: query over a materialized view
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# accessed by a key
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#
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CREATE TABLE t1 (a int) ;
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INSERT INTO t1 VALUES (8);
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CREATE TABLE t2 (a int, b int) ;
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INSERT INTO t2 VALUES
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(262, NULL), (253, 190), (260, NULL), (250, 163), (188, 8),
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(257,200), (256, NULL), (255, 8), (249, NULL), (259, 7);
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CREATE VIEW v1 AS SELECT a, MIN(b) AS b FROM t2 GROUP BY a;
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EXPLAIN
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SELECT * FROM v1, t1 WHERE v1.b=t1.a ORDER BY v1.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 system NULL NULL NULL NULL 1 Using filesort
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1 PRIMARY <derived2> ref key0 key0 5 const 1 Using where
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2 DERIVED t2 ALL NULL NULL NULL NULL 10 Using temporary; Using filesort
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SELECT * FROM v1, t1 WHERE v1.b=t1.a ORDER BY v1.a;
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a b a
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188 8 8
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255 8 8
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DROP VIEW v1;
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DROP TABLE t1,t2;
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#
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# LP bug #800085: crash with a query using a simple derived table
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# (fixed by the patch for bug 798621)
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#
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CREATE TABLE t1 (f1 int, f2 varchar(32)) ;
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INSERT INTO t1 VALUES (NULL,'j'), (8,'c');
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CREATE TABLE t2 (f1 int);
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INSERT INTO t2 VALUES (1), (5);
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SELECT DISTINCT t.f1 FROM (SELECT * FROM t1) AS t, t2
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WHERE t.f2='s' AND t.f2 LIKE '%a%' OR t.f1<>0 ORDER BY t.f2;
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f1
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8
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DROP TABLE t1, t2;
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#
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# BUG##806524: Assertion `join->best_read < 1.7976931348623157e+308 with table_elimination=on and derived_merge=on
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#
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CREATE TABLE t1 ( f4 int) ;
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CREATE TABLE t2 ( f4 int) ;
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CREATE TABLE t3 ( f1 int NOT NULL , PRIMARY KEY (f1)) ;
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CREATE TABLE t4 ( f2 int, f4 int) ;
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SELECT *
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FROM ( SELECT * FROM t1 ) AS alias1
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RIGHT JOIN (
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t2 AS alias2
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LEFT JOIN (
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SELECT t4.*
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FROM ( SELECT * FROM t3 ) AS SQ1_alias1
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RIGHT JOIN t4
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ON t4.f2 = SQ1_alias1.f1
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) AS alias3
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ON alias3.f4 != 0
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) ON alias3.f4 != 0;
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f4 f4 f2 f4
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drop table t1,t2,t3,t4;
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#
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# LP BUG#910123 MariaDB 5.3.3 causes 1093 error on Drupal
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# Fix: force materialization in case of conflict
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#
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SET optimizer_switch='derived_merge=on';
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CREATE TABLE t1 ( i INT );
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INSERT INTO t1 VALUES ( (SELECT 1 FROM ( SELECT * FROM t1 ) as a) );
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drop table t1;
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set optimizer_switch=@save_optimizer_switch;
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set optimizer_switch=@exit_optimizer_switch;
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