drop table if exists t1, t2, t3;
create table t1 (_id int, a int, unique key (_id) using hash);
insert into t1 values(null, 100);
insert into t1 values(null, 100);
insert into t1 values(null, 100);
insert into t1 values(null, 100);
select * from t1;
_id	a
1	100
2	100
3	100
4	100
select * from t1 where _id = 2;
_id	a
2	100
select * from t1 where _id = 20;
_id	a
drop table t1;
