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drop table if exists t0, t1, t2, t10, t11, t12;
create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1(a int, b int);
insert into t1 values (0,0),(1,1),(2,2);
create table t2 as select * from t1;
create table t11(a int, b int);
create table t10 (pk int, a int, primary key(pk));
insert into t10 select a,a from t0;
create table t12 like t10;
insert into t12 select * from t10;
Flattened because of dependency, t10=func(t1)
explain select * from t1 where a in (select pk from t10);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where
2 SUBQUERY t10 ALL NULL NULL NULL NULL 10
select * from t1 where a in (select pk from t10);
a b
0 0
1 1
2 2
A confluent case of dependency
explain select * from t1 where a in (select a from t10 where pk=12);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where
2 SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
select * from t1 where a in (select a from t10 where pk=12);
a b
An empty table inside
explain select * from t1 where a in (select a from t11);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where
2 SUBQUERY t11 ALL NULL NULL NULL NULL 0
select * from t1 where a in (select a from t11);
a b
explain select * from t1 where a in (select pk from t10) and b in (select pk from t10);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where
3 SUBQUERY t10 ALL NULL NULL NULL NULL 10
2 SUBQUERY t10 ALL NULL NULL NULL NULL 10
select * from t1 where a in (select pk from t10) and b in (select pk from t10);
a b
0 0
1 1
2 2
flattening a nested subquery
explain select * from t1 where a in (select pk from t10 where t10.a in (select pk from t12));
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 Using where
2 SUBQUERY t10 ALL NULL NULL NULL NULL 10 Using where
3 SUBQUERY t12 ALL NULL NULL NULL NULL 10
select * from t1 where a in (select pk from t10 where t10.a in (select pk from t12));
a b
0 0
1 1
2 2
flattening subquery w/ several tables
explain extended select * from t1 where a in (select t10.pk from t10, t12 where t12.pk=t10.a);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 3 100.00 Using where
2 SUBQUERY t10 ALL NULL NULL NULL NULL 10 100.00
2 SUBQUERY t12 eq_ref PRIMARY PRIMARY 4 test.t10.a 1 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where <in_optimizer>(`test`.`t1`.`a`,`test`.`t1`.`a` in ( <materialize> (select `test`.`t10`.`pk` AS `pk` from `test`.`t10` join `test`.`t12` where (`test`.`t12`.`pk` = `test`.`t10`.`a`) ), <primary_index_lookup>(`test`.`t1`.`a` in <temporary table> on distinct_key)))
subqueries within outer joins go into ON expr.
select * from
t1 left join t2 on (t2.a= t1.a and t2.a in (select pk from t10))
where t1.a < 5;
a b a b
0 0 0 0
1 1 1 1
2 2 2 2
insert into t1 select (A.a + 10 * B.a),1 from t0 A, t0 B;
explain extended select * from t1 where a in (select pk from t10 where pk<3);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 103 100.00 Using where
2 SUBQUERY t10 ALL PRIMARY NULL NULL NULL 10 100.00 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where <in_optimizer>(`test`.`t1`.`a`,`test`.`t1`.`a` in ( <materialize> (select `test`.`t10`.`pk` AS `pk` from `test`.`t10` where (`test`.`t10`.`pk` < 3) ), <primary_index_lookup>(`test`.`t1`.`a` in <temporary table> on distinct_key)))
drop table t0, t1;
drop table t10, t11, t12;
drop table t2;
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