mariadb/mysql-test/r/table_elim.result

drop table if exists t0, t1, t2, t3;
create table t1 (a int);
insert into t1 values (0),(1),(2),(3);
create table t0 as select * from t1;
create table t2 (a int primary key, b int) 
as select a, a as b from t1 where a in (1,2);
create table t3 (a int primary key, b int) 
as select a, a as b from t1 where a in (1,3);
# This will be  eliminated:
explain select t1.a from t1 left join t2 on t2.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	100.00	
Warnings:
Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where 1
select t1.a from t1 left join t2 on t2.a=t1.a;
a
0
1
2
3
# This will not be eliminated as t2.b is in in select list:
explain select * from t1 left join t2 on t2.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	
# This will not be eliminated as t2.b is in in order list:
explain select t1.a from t1 left join t2 on t2.a=t1.a order by t2.b;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	
# This will not be eliminated as t2.b is in group list:
explain select t1.a from t1 left join t2 on t2.a=t1.a group by t2.b;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	
# This will not be eliminated as t2.b is in the WHERE
explain select t1.a from t1 left join t2 on t2.a=t1.a where t2.b < 3 or t2.b is null;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	Using where
# Elimination of multiple tables:
explain select t1.a from t1 left join (t2 join t3) on t2.a=t1.a and t3.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
# Elimination of multiple tables (2):
explain select t1.a from t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and t3.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
# Elimination when done within an outer join nest:
explain extended
select t0.*
from
t0 left join (t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
t3.a=t1.a) on t0.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	4	100.00	
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	100.00	
Warnings:
Note	1003	select `test`.`t0`.`a` AS `a` from `test`.`t0` left join (`test`.`t1`) on((`test`.`t0`.`a` = `test`.`t1`.`a`)) where 1
# Elimination with aggregate functions
explain select count(*) from t1 left join t2 on t2.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
explain select count(1) from t1 left join t2 on t2.a=t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
explain select count(1) from t1 left join t2 on t2.a=t1.a group by t1.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
This must not use elimination:
explain select count(1) from t1 left join t2 on t2.a=t1.a group by t2.a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort
1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	Using index
drop table t0, t1, t2, t3;