drop table if exists t1,t2;
create table t1(n int);
insert into t1 values (1);
lock tables t1 write;
 update low_priority t1 set n = 4;
 select n from t1;
unlock tables;
n
4
drop table t1;
create table t1(n int);
insert into t1 values (1);
lock tables t1 read;
 update low_priority t1 set n = 4;
 select n from t1;
unlock tables;
n
1
drop table t1;
create table t1 (a int, b int);
create table t2 (c int, d int);
insert into t1 values(1,1);
insert into t1 values(2,2);
insert into t2 values(1,2);
lock table t1 read;
 update t1,t2 set c=a where b=d;
select c from t2;
c
2
drop table t1;
drop table t2;
create table t1 (a int);
create table t2 (a int);
lock table t1 write, t2 write;
 insert t1 select * from t2;
drop table t2;
ERROR 42S02: Table 'test.t2' doesn't exist
drop table t1;
create table t1(a int);
lock tables t1 write;
show columns from t1;
Field	Type	Null	Key	Default	Extra
a	int(11)	YES		NULL	
unlock tables;
drop table t1;