drop table if exists t1, t2, t3;
create table t1 (kill_id int);
insert into t1 values(connection_id());
select ((@id := kill_id) - kill_id) from t1;
((@id := kill_id) - kill_id)
0
kill @id;
select ((@id := kill_id) - kill_id) from t1;
((@id := kill_id) - kill_id)
0
select @id != connection_id();
@id != connection_id()
1
select 4;
4
4
drop table t1;
create table t1 (id int primary key);
create table t2 (id int unsigned not null);
insert into t2 select id from t1;
create table t3 (kill_id int);
insert into t3 values(connection_id());
 select id from t1 where id in (select distinct id from t2);
select ((@id := kill_id) - kill_id) from t3;
((@id := kill_id) - kill_id)
0
kill @id;
ERROR 08S01: Server shutdown in progress
drop table t1, t2, t3;
select get_lock("a", 10);
get_lock("a", 10)
1
 select get_lock("a", 10);
get_lock("a", 10)
NULL
select 1;
1
1
select RELEASE_LOCK("a");
RELEASE_LOCK("a")
1