drop table if exists t1;
create table t1 (id integer, x integer) engine=INNODB;
insert into t1 values(0, 0);
set autocommit=0;
SELECT * from t1 where id = 0 FOR UPDATE;
id	x
0	0
set autocommit=0;
lock table t1 write;
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
commit;
update t1 set x=2 where id = 0;
commit;
unlock tables;
select * from t1;
id	x
0	2
commit;
drop table t1;