mysql - 如何在 mysql 中使用删除级联？

Question

我有一个组件数据库。每个组件都属于特定类型。这意味着组件和类型之间存在多对一的关系。当我删除一个类型时，我想删除所有具有该类型外键的组件。但是如果我没记错的话，级联删除会在删除组件时删除类型。有什么办法可以做我描述的吗？

Answer 1

这是您要包含在组件表中的内容。

CREATE TABLE `components` (
    `id` int(10) unsigned NOT NULL auto_increment,
    `typeId` int(10) unsigned NOT NULL,
    `moreInfo` VARCHAR(32), 
    -- etc
    PRIMARY KEY (`id`),
    KEY `type` (`typeId`)
    CONSTRAINT `myForeignKey` FOREIGN KEY (`typeId`)
      REFERENCES `types` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
)

请记住，您需要使用 InnoDB 存储引擎：默认的 MyISAM 存储引擎不支持外键。

Answer 2

使用这个 sql

DELETE T1, T2 FROM T1 INNER JOIN T2 ON T1.key = T2.key WHERE 条件

Answer 3

您必须将外键约束定义为 ON DELETE CASCADE。

注意：您需要使用 InnoDB 存储引擎，默认的 MyISAM 存储引擎不支持外键关系。

CREATE TABLE `table2` (
`id` int(11) NOT NULL auto_increment,
`name` int(11) NOT NULL,

PRIMARY KEY (`id`),
KEY `ids` (`ids`)
CONSTRAINT `foreign` FOREIGN KEY (`ids`)
  REFERENCES `table2` (`ids`) ON DELETE CASCADE ON UPDATE CASCADE
)

Answer 4

Step 1. Create the buildings table:

CREATE TABLE buildings (
  building_no INT PRIMARY KEY AUTO_INCREMENT,
  building_name VARCHAR(255) NOT NULL,
  address VARCHAR(255) NOT NULL
);

Step 2. Create the rooms table:

CREATE TABLE rooms (
  room_no INT PRIMARY KEY AUTO_INCREMENT,
  room_name VARCHAR(255) NOT NULL,
  building_no INT NOT NULL,
  FOREIGN KEY (building_no)
    REFERENCES buildings (building_no)
    ON DELETE CASCADE
);

Notice that the ON DELETE CASCADE  clause at the end of the foreign key constraint 
definition.