變更表/解鎖

Question

有人能解釋爲什麼我收到此錯誤：

Table 'last' was not locked with LOCK TABLES 

這裏是陸續執行一個查詢：

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; 

上線的誤差點，增加了列（id），但是，如果我把解鎖語句之後刪除 - 一切正常，沒有錯誤。是不是真的，我不能最後解鎖一張桌子？它給我的錯誤與其他表，說同樣的事情

Answer 1

見http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html「表不是用LOCK TABLES鎖定」：

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」.