drop table if exists t0, t1, t2, t3; drop view if exists v1, v2; 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 Using where 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; create table t0 ( id integer, primary key (id)); create table t1 ( id integer, attr1 integer, primary key (id), key (attr1) ); create table t2 ( id integer, attr2 integer, fromdate date, primary key (id, fromdate), key (attr2,fromdate) ); insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9); insert into t0 select A.id + 10*B.id from t0 A, t0 B where B.id > 0; insert into t1 select id, id from t0; insert into t2 select id, id, date_add('2009-06-22', interval id day) from t0; insert into t2 select id, id+1, date_add('2008-06-22', interval id day) from t0; create view v1 as select f.id, a1.attr1, a2.attr2 from t0 f left join t1 a1 on a1.id=f.id left join t2 a2 on a2.id=f.id and a2.fromdate=(select MAX(fromdate) from t2 where id=a2.id); create view v2 as select f.id, a1.attr1, a2.attr2 from t0 f left join t1 a1 on a1.id=f.id left join t2 a2 on a2.id=f.id and a2.fromdate=(select MAX(fromdate) from t2 where id=f.id); This should use one table: explain select id from v1 where id=2; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY f const PRIMARY PRIMARY 4 const 1 Using index This should use one table: explain extended select id from v1 where id in (1,2,3,4); id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY f range PRIMARY PRIMARY 4 NULL 4 100.00 Using where; Using index Warnings: Note 1276 Field or reference 'test.a2.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` where (`f`.`id` in (1,2,3,4)) This should use facts and a1 tables: explain extended select id from v1 where attr1 between 12 and 14; id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY a1 range PRIMARY,attr1 attr1 5 NULL 2 100.00 Using index condition; Using MRR 1 PRIMARY f eq_ref PRIMARY PRIMARY 4 test.a1.id 1 100.00 Using index Warnings: Note 1276 Field or reference 'test.a2.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` join `test`.`t1` `a1` where ((`f`.`id` = `a1`.`id`) and (`a1`.`attr1` between 12 and 14)) This should use facts, a2 and its subquery: explain extended select id from v1 where attr2 between 12 and 14; id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY a2 range PRIMARY,attr2 attr2 5 NULL 5 100.00 Using index condition; Using where; Using MRR 1 PRIMARY f eq_ref PRIMARY PRIMARY 4 test.a2.id 1 100.00 Using index 3 DEPENDENT SUBQUERY t2 ref PRIMARY PRIMARY 4 test.a2.id 2 100.00 Using index Warnings: Note 1276 Field or reference 'test.a2.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` join `test`.`t2` `a2` where ((`f`.`id` = `a2`.`id`) and (`a2`.`attr2` between 12 and 14) and (`a2`.`fromdate` = (select max(`test`.`t2`.`fromdate`) AS `MAX(fromdate)` from `test`.`t2` where (`test`.`t2`.`id` = `a2`.`id`)))) This should use one table: explain select id from v2 where id=2; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY f const PRIMARY PRIMARY 4 const 1 Using index This should use one table: explain extended select id from v2 where id in (1,2,3,4); id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY f range PRIMARY PRIMARY 4 NULL 4 100.00 Using where; Using index Warnings: Note 1276 Field or reference 'test.f.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` where (`f`.`id` in (1,2,3,4)) This should use facts and a1 tables: explain extended select id from v2 where attr1 between 12 and 14; id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY a1 range PRIMARY,attr1 attr1 5 NULL 2 100.00 Using index condition; Using MRR 1 PRIMARY f eq_ref PRIMARY PRIMARY 4 test.a1.id 1 100.00 Using index Warnings: Note 1276 Field or reference 'test.f.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` join `test`.`t1` `a1` where ((`f`.`id` = `a1`.`id`) and (`a1`.`attr1` between 12 and 14)) This should use facts, a2 and its subquery: explain extended select id from v2 where attr2 between 12 and 14; id select_type table type possible_keys key key_len ref rows filtered Extra 1 PRIMARY a2 range PRIMARY,attr2 attr2 5 NULL 5 100.00 Using index condition; Using MRR 1 PRIMARY f eq_ref PRIMARY PRIMARY 4 test.a2.id 1 100.00 Using where; Using index 3 DEPENDENT SUBQUERY t2 ref PRIMARY PRIMARY 4 test.f.id 2 100.00 Using index Warnings: Note 1276 Field or reference 'test.f.id' of SELECT #3 was resolved in SELECT #1 Note 1003 select `f`.`id` AS `id` from `test`.`t0` `f` join `test`.`t2` `a2` where ((`f`.`id` = `a2`.`id`) and (`a2`.`attr2` between 12 and 14) and (`a2`.`fromdate` = (select max(`test`.`t2`.`fromdate`) AS `MAX(fromdate)` from `test`.`t2` where (`test`.`t2`.`id` = `f`.`id`)))) drop view v1, v2; drop table t0, t1, t2; create table t1 (a int); insert into t1 values (0),(1),(2),(3); create table t2 (pk1 int, pk2 int, pk3 int, col int, primary key(pk1, pk2, pk3)); insert into t2 select a,a,a,a from t1; This must use only t1: explain select t1.* from t1 left join t2 on t2.pk1=t1.a and t2.pk2=t2.pk1+1 and t2.pk3=t2.pk2+1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 4 This must use only t1: explain select t1.* from t1 left join t2 on t2.pk1=t1.a and t2.pk3=t2.pk1+1 and t2.pk2=t2.pk3+1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 4 This must use both: explain select t1.* from t1 left join t2 on t2.pk1=t1.a and t2.pk3=t2.pk1+1 and t2.pk2=t2.pk3+t2.col; 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 ref PRIMARY PRIMARY 4 test.t1.a 1 Using where This must use only t1: explain select t1.* from t1 left join t2 on t2.pk2=t1.a and t2.pk1=t2.pk2+1 and t2.pk3=t2.pk1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 4 drop table t1, t2; create table t1 (pk int primary key, col int); insert into t1 values (1,1),(2,2); create table t2 like t1; insert into t2 select * from t1; create table t3 like t1; insert into t3 select * from t1; explain select t1.* from t1 left join ( t2 left join t3 on t3.pk=t2.col) on t2.col=t1.col; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 1 SIMPLE t2 ALL NULL NULL NULL NULL 2 Using where explain select t1.*, t2.* from t1 left join (t2 left join t3 on t3.pk=t2.col) on t2.pk=t1.col; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 1 SIMPLE t2 eq_ref PRIMARY PRIMARY 4 test.t1.col 1 explain select t1.* from t1 left join ( t2 left join t3 on t3.pk=t2.col or t3.pk=t2.col) on t2.col=t1.col or t2.col=t1.col; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 1 SIMPLE t2 ALL NULL NULL NULL NULL 2 Using where explain select t1.*, t2.* from t1 left join (t2 left join t3 on t3.pk=t2.col or t3.pk=t2.col) on t2.pk=t1.col or t2.pk=t1.col; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 2 1 SIMPLE t2 eq_ref PRIMARY PRIMARY 4 test.t1.col 1 drop table t1, t2, t3; # # Check things that look like functional dependencies but really are not # create table t1 (a char(10) character set latin1 collate latin1_general_ci primary key); insert into t1 values ('foo'); insert into t1 values ('bar'); create table t2 (a char(10) character set latin1 collate latin1_general_cs primary key); insert into t2 values ('foo'); insert into t2 values ('FOO'); this must not use table elimination: explain select t1.* from t1 left join t2 on t2.a='foo' collate latin1_general_ci; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 10 NULL 2 Using index 1 SIMPLE t2 index PRIMARY PRIMARY 10 NULL 2 Using where; Using index this must not use table elimination: explain select t1.* from t1 left join t2 on t2.a=t1.a collate latin1_general_ci; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 10 NULL 2 Using index 1 SIMPLE t2 ALL PRIMARY NULL NULL NULL 2 Range checked for each record (index map: 0x1) drop table t1,t2; create table t1 (a int primary key); insert into t1 values (1),(2); create table t2 (a char(10) primary key); insert into t2 values ('1'),('1.0'); this must not use table elimination: explain select t1.* from t1 left join t2 on t2.a=1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 2 Using index 1 SIMPLE t2 index PRIMARY PRIMARY 10 NULL 2 Using where; Using index this must not use table elimination: explain select t1.* 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 index NULL PRIMARY 4 NULL 2 Using index 1 SIMPLE t2 ALL PRIMARY NULL NULL NULL 2 Range checked for each record (index map: 0x1) drop table t1, t2; create table t1 (a char(10) primary key); insert into t1 values ('foo'),('bar'); create table t2 (a char(10), unique key(a(2))); insert into t2 values ('foo'),('bar'); explain select t1.* 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 index NULL PRIMARY 10 NULL 2 Using index 1 SIMPLE t2 ref a a 3 test.t1.a 2 Using where drop table t1, t2; # # check UPDATE/DELETE that look like they could be eliminated # create table t1 (a int primary key, b int); insert into t1 values (1,1),(2,2),(3,3); create table t2 like t1; insert into t2 select * from t1; update t1 left join t2 using (a) set t2.a=t2.a+100; select * from t1; a b 1 1 2 2 3 3 select * from t2; a b 101 1 102 2 103 3 delete from t2; insert into t2 select * from t1; delete t2 from t1 left join t2 using (a); select * from t1; a b 1 1 2 2 3 3 select * from t2; a b drop table t1, t2; # # Tests with various edge-case ON expressions # create table t1 (a int, b int, c int, d int); insert into t1 values (0,0,0,0),(1,1,1,1),(2,2,2,2),(3,3,3,3); create table t2 (pk int primary key, b int) as select a as pk, a as b from t1 where a in (1,2); create table t3 (pk1 int, pk2 int, b int, unique(pk1,pk2)); insert into t3 select a as pk1, a as pk2, a as b from t1 where a in (1,3); explain select t1.a from t1 left join t2 on t2.pk=t1.a and t2.b