曾经这是 MySQL的一个bug,但是现在只是MySQL的一个不友好的地方。
例子如下:
mysql> ALTER TABLE ruler.test2child DROP FOREIGN KEY test;
ERROR 1025 : Error on rename of ''./ruler/test2child'' to ''./ruler/#sql2-298-8f'' (errno:
152)
这里并不是不能 删除外键,而是使用了错误的外键名称,但是MySQL报的错实在离谱。
正确的错误信息要如下查询才能知道:
mysql> show innodb status;
------------------------
LATEST FOREIGN KEY ERROR
------------------------
071222 20:48:26 Error in dropping of a foreign key constraint of table
"ruler"."test2child",
in SQL command
ALTER TABLE ruler.test2child DROP FOREIGN KEY test
Cannot find a constraint with the given id "test".
另外外键的其他操作也有类似情况:
比如外键 新建报错:
Can''t create table ''ruler.#sql-298_92'' (errno: 150)
show innodb status;
------------------------
LATEST FOREIGN KEY ERROR
------------------------
071222 20:18:57 Error in foreign key constraint of table ruler/#sql-298_8d:
FOREIGN KEY (test2code) REFERENCES ruler.test2 (test) on delete set null:
You have defined a SET NULL condition though some of the
columns are defined as NOT NULL.