对于MyISAM表，加的锁是表级锁；写操作会阻塞读操作，读操作会阻塞写操作，写操作会阻塞写操作；读操作不会阻塞读操作。 测试一，会话①的 读操作阻塞会话②的写操作 会话① mysql> create table t2(id tinyint(3) unsigned not null auto_increment,     ->  name varchar(10) not null,     ->  primary key(id))     ->  engine=myisam auto_increment=8 default charset=gbk; Query OK, 0 rows affected (0.03 sec) mysql> insert into t2(name) values('Neo'); Query OK, 1 row affected (0.03 sec) mysql> insert into t2(name) values('Trinity'); Query OK, 1 row affected (0.00 sec) mysql> select * from t2; +----+---------+ | id | name    | +----+---------+ |  8 | Neo     | |  9 | Trinity | +----+---------+ 2 rows in set (0.00 sec) mysql> desc t2; +-------+---------------------+------+-----+---------+----------------+ | Field | Type                | Null | Key | Default | Extra          | +-------+---------------------+------+-----+---------+----------------+ | id    | tinyint(3) unsigned | NO   | PRI | NULL    | auto_increment | | name  | varchar(10)         | NO   |     | NULL    |                | +-------+---------------------+------+-----+---------+----------------+ 2 rows in set (0.09 sec) 为表增加读锁 mysql> lock table t2 read; Query OK, 0 rows affected (0.00 sec) 会话② mysql> select * from t2; +----+---------+ | id | name    | +----+---------+ |  8 | Neo     | |  9 | Trinity | +----+---------+ 2 rows in set (0.00 sec) 会话会处于等待状态 mysql> update t2 set name='James' where id=5; 会话① mysql> show processlist; +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+---------------------------------------+ | Id | User            | Host      | db   | Command | Time   | State                                                                       | Info                                  | +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+---------------------------------------+ |  1 | system user     |           | NULL | Connect | 748155 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL                                  | |  2 | system user     |           | NULL | Connect | 748156 | Connecting to master                                                        | NULL                                  | | 13 | event_scheduler | localhost | NULL | Daemon  | 600105 | Waiting on empty queue                                                      | NULL                                  | | 74 | neo             | localhost | fire | Query   |      0 | NULL                                                                        | show processlist                      | | 75 | neo             | localhost | fire | Query   |     83 | Waiting for table level lock                                                | update t2 set name='James' where id=5 | +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+---------------------------------------+ 5 rows in set (0.00 sec) mysql> unlock tables; Query OK, 0 rows affected (0.00 sec) 会话② mysql> update t2 set name='James' where id=5; Query OK, 0 rows affected (1 min 48.96 sec) Rows matched: 0  Changed: 0  Warnings: 0 测试二，会话①的写 操作阻塞会话②的读操作 会话① mysql> lock table t2 write; Query OK, 0 rows affected (0.00 sec) mysql> insert into t2(name) values('Jack'); Query OK, 1 row affected (0.01 sec) mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> show processlist; +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+------------------+ | Id | User            | Host      | db   | Command | Time   | State                                                                       | Info             | +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+------------------+ |  1 | system user     |           | NULL | Connect | 748422 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL             | |  2 | system user     |           | NULL | Connect | 748423 | Connecting to master                                                        | NULL             | | 13 | event_scheduler | localhost | NULL | Daemon  | 600372 | Waiting on empty queue                                                      | NULL             | | 74 | neo             | localhost | fire | Query   |      0 | NULL                                                                        | show processlist | | 75 | neo             | localhost | fire | Query   |      2 | Waiting for table metadata lock                                             | select * from t2 | +----+-----------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+------------------+ 5 rows in set (0.00 sec) 会话② 查询会阻塞 mysql> select * from t2; 会话① mysql> unlock tables; Query OK, 0 rows affected (0.00 sec) 会话② mysql> select * from t2; +----+---------+ | id | name    | +----+---------+ |  8 | Neo     | |  9 | Trinity | | 10 | Jack    | +----+---------+ 3 rows in set (47.89 sec)

当同一个会话中，锁定一张表后，查询另外一张表会报错

mysql> lock table test read;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test where id=80;

+------+------+

| id   | name |

+------+------+

|   80 | Lily |

+------+------+

1 row in set (0.00 sec)

mysql> select * from t70;

ERROR 1100 (HY000): Table 't70' was not locked with LOCK TABLES

使用表的别名会报错

mysql> lock table test read;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test t where id=80;

ERROR 1100 (HY000): Table 't' was not locked with LOCK TABLES

需要对别名进行锁定

mysql> lock table test t read;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from test t where id=80;

+------+------+

| id   | name |

+------+------+

|   80 | Kame |

+------+------+

1 row in set (0.00 sec)

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