drop table if exists t1,t2;
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;
update t1 set x=2 where id = 0;
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
commit;
commit;
select * from t1;
id	x
0	2
commit;
drop table t1;
create table t1 (id integer, x integer) engine=INNODB;
create table t2 (b integer, a integer) engine=INNODB;
insert into t1 values(0, 0), (300, 300);
insert into t2 values(0, 10), (1, 20), (2, 30);
commit;
set autocommit=0;
select * from t2;
b	a
0	10
1	20
2	30
update t2 set a=100 where b=(SELECT x from t1 where id = b FOR UPDATE);
select * from t2;
b	a
0	100
1	20
2	30
select * from t1;
id	x
0	0
300	300
set autocommit=0;
update t1 set x=2 where id = 0;
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
300	300
commit;
commit;
select * from t1;
id	x
0	2
300	300
commit;
drop table t1, t2;
create table t1 (id integer, x integer) engine=INNODB;
create table t2 (b integer, a integer) engine=INNODB;
insert into t1 values(0, 0), (300, 300);
insert into t2 values(0, 0), (1, 20), (2, 30);
commit;
select a,b from t2 UNION SELECT id, x from t1 FOR UPDATE;
a	b
0	0
20	1
30	2
300	300
select * from t2;
b	a
0	0
1	20
2	30
select * from t1;
id	x
0	0
300	300
update t2 set a=2 where b = 0;
select * from t2;
b	a
0	2
1	20
2	30
update t1 set x=2 where id = 0;
update t1 set x=1 where id = 0;
select * from t1;
id	x
0	1
300	300
commit;
commit;
select * from t1;
id	x
0	2
300	300
commit;
drop table t1, t2;
