DROP CONSTRAINT无法找到约束

Question

我试图放弃一个约束：

USE `mydb`;

BEGIN;
ALTER TABLE `mydb` DROP CONSTRAINT `myconstraint`;
COMMIT;

并回复：

ERROR 1091 (42000) at line 6: Can't DROP CONSTRAINT `myconstraint`; check that it exists

但存在约束：

MariaDB [(mydb)]> select * from information_schema.table_constraints WHERE table_name = 'mytable';
+--------------------+-------------------+---------------------------------------------------------------+--------------+-----------------+-----------------+
| CONSTRAINT_CATALOG | CONSTRAINT_SCHEMA | CONSTRAINT_NAME                                               | TABLE_SCHEMA | TABLE_NAME      | CONSTRAINT_TYPE |
+--------------------+-------------------+---------------------------------------------------------------+--------------+-----------------+-----------------+
| def                | mydb              | PRIMARY                                                       | mydb         | mytable         | PRIMARY KEY     |
| def                | mydb              | name                                                          | mydb         | mytable         | UNIQUE          |
| def                | mydb              | myconstraint                                                  | mydb         | mytable         | FOREIGN KEY     |
+--------------------+-------------------+---------------------------------------------------------------+--------------+-----------------+-----------------+

我究竟做错了什么？

Answer 1

我认为你混淆“架构”（又名“数据库”）和“表格”：ALTER TABLE mytable ...

Answer 2

问题是MariaDB（MySql？）不允许使用语法DROP CONSTRAINT删除外键约束。它必须像这样删除：

ALTER TABLE `mytable` DROP FOREIGN KEY `myconstraint`;