7.1. 排他锁
下面做作一个实验，验证锁的效果
终端一,首先进入事务状态然后运行下面语句
mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from t1 where id='3' for update; +----+--------+---------------------+---------------------+ | id | name | ctime | mtime | +----+--------+---------------------+---------------------+ | 3 | test | 0000-00-00 00:00:00 | 2013-01-14 13:05:41 | +----+--------+---------------------+---------------------+ 1 row in set (0.00 sec)
终端二, 查询表中数据
mysql> select * from t1; +----+--------+---------------------+---------------------+ | id | name | ctime | mtime | +----+--------+---------------------+---------------------+ | 1 | neo | 0000-00-00 00:00:00 | 2013-01-14 13:00:00 | | 2 | zen | 0000-00-00 00:00:00 | 2013-01-14 13:00:43 | | 3 | test | 0000-00-00 00:00:00 | 2013-01-14 13:05:41 | +----+--------+---------------------+---------------------+ 3 rows in set (0.00 sec)
增加“for update”查询非锁定记录
mysql> select * from t1 where id=2 for update; +----+------+---------------------+---------------------+ | id | name | ctime | mtime | +----+------+---------------------+---------------------+ | 2 | zen | 0000-00-00 00:00:00 | 2013-01-14 13:00:43 | +----+------+---------------------+---------------------+ 1 row in set (0.00 sec)
查询被锁定记录
mysql> select * from t1 where id=3 for update; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
查询所有记录，因为记录中包含了id=3那条，所以也不允许查询。
mysql> select * from t1 for update; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
测试修改记录
mysql> UPDATE `t1` SET `name`='testaa' WHERE `id`=3; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
提示
在没有出现ERROR 1205 (HY000)的这段时间，只要终端一中执行commit,rollback.终端二中的语句就会运行。