select (select 2);
drop table if exists t1,t2,t3,t4,t5;
create table t1 (a int);
create table t2 (a int, b int);
create table t3 (a int);
create table t4 (a int, b int);
insert into t1 values (2);
insert into t2 values (1,7),(2,7);
insert into t4 values (4,8),(3,8),(5,9);
select (select a from t1 where t1.a=t2.a), a from t2;
select (select a from t1 where t1.a=t2.b), a from t2;
select (select a from t1), a from t2;
select (select a from t3), a from t2;
select * from t2 where t2.a=(select a from t1);
insert into t3 values (6),(7),(3);
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1);
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1) 
union (select * from t4 order by a limit 2) limit 3;
select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1) 
union (select * from t4 where t4.b=(select max(t2.a)*4 from t2) order by a);
select (select a from t3 where a<t2.a*4 order by 1 desc limit 1), a from t2;
select (select t3.a from t3 where a<8 order by 1 desc limit 1), a from 
(select * from t2 where a>1) as tt;
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3) order by 1 desc limit 1);
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3 where t3.a > t1.a) order by 1 desc limit 1);
select * from t1 where t1.a=(select t2.a from t2 where t2.b=(select max(a) from t3 where t3.a < t1.a) order by 1 desc limit 1);
select b,(select avg(t2.a+(select min(t3.a) from t3 where t3.a >= t4.a)) from t2) from t4;
select * from t3 where exists (select * from t2 where t2.b=t3.a);
select * from t3 where not exists (select * from t2 where t2.b=t3.a);
insert into t4 values (12,7),(1,7),(10,9),(9,6),(7,6),(3,9);
select b,max(a) as ma from t4 group by b having b < (select max(t2.a)
from t2 where t2.b=t4.b);
select b,max(a) as ma from t4 group by b having b >= (select max(t2.a)
from t2 where t2.b=t4.b);
create table t5 (a int);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
insert into t5 values (5);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
insert into t5 values (2);
select (select a from t1 where t1.a=t2.a union select a from t5 where t5.a=t2.a), a from t2;
-- error 1230
select (select a from t1 where t1.a=t2.a union all select a from t5 where t5.a=t2.a), a from t2;
drop table t1,t2,t3,t4,t5;