说明
1、对MyISAM表的写操作（加写锁），会阻塞其他进程对同一表的读和写操作。
2、只有当写锁释放后，才会执行其他进程的读写操作。在锁释放前不能写其他表。
实例
Transaction-A mysql> set autocommit=0; Query OK, 0 rows affected (0.05 sec) mysql> lock table myisam_lock write; Query OK, 0 rows affected (0.03 sec) mysql> update myisam_lock set v='2001' where k='2'; Query OK, 1 row affected (0.00 sec) mysql> select * from myisam_lock; 9 rows in set (0.00 sec) mysql> update innodb_lock set v='1001' where k='1'; ERROR 1100 (HY000): Table 'innodb_lock' was not locked with LOCK TABLES mysql> unlock tables; Query OK, 0 rows affected (0.00 sec)
