set global innodb_table_locks=1;
select @@innodb_table_locks;
@@innodb_table_locks
1
drop table if exists t1;
set @@innodb_table_locks=1;
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;
set @@innodb_table_locks=0;
create table t1 (id integer primary key, x integer) engine=INNODB;
insert into t1 values(0, 0),(1,1),(2,2);
commit;
SELECT * from t1 where id = 0 FOR UPDATE;
id	x
0	0
set autocommit=0;
set @@innodb_table_locks=0;
lock table t1 write;
update t1 set x=10 where id = 2;
SELECT * from t1 where id = 2;
id	x
2	2
UPDATE t1 set x=3 where id = 2;
commit;
SELECT * from t1;
id	x
0	0
1	1
2	3
commit;
unlock tables;
commit;
select * from t1;
id	x
0	0
1	1
2	10
drop table t1;
