mysql - 使用锁定/解锁更改表

Question

有人可以解释为什么我会收到此错误:

Table 'last' was not locked with LOCK TABLES

这是一个接一个执行的查询:

LOCK TABLES last WRITE;
DELETE FROM last WHERE id < '30';
ALTER TABLE last DROP id;
ALTER TABLE last ADD COLUMN `id` SMALLINT(5) UNSIGNED NOT NULL AUTO_INCREMENT FIRST, ADD PRIMARY KEY (`id`);

UNLOCK TABLES;

错误点在添加列 (id) 的行上，但是如果我在删除之后放置解锁语句 - 一切正常，没有错误。我真的不能最后解锁一张 table 吗？它给了我其他表的错误，说同样的话“表没有用锁表锁定”

Answer 1

参见 http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html :

If you use ALTER TABLE on a locked table, it may become unlocked. For example, if you attempt a second ALTER TABLE operation, the result may be an error Table 'tbl_name' was not locked with LOCK TABLES. To handle this, lock the table again prior to the second alteration. See also Section C.5.7.1, “Problems with ALTER TABLE”.