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;

它的回复是：

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

但约束是存在的：

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     |
+--------------------+-------------------+---------------------------------------------------------------+--------------+-----------------+-----------------+

我做错了什么？

Answer 1

该问题记录在https://jira.mariadb.org/browse/MDEV-17599.它在版本10.2.22和10.3.13（11-02-2019）中得到了修复。我建议更新MariaDB版本，或者像@volingas所写的sintax：

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

Answer 2

我认为你混淆了“模式”（又名“数据库”）和“表”）：altertablemytable

Answer 3

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

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