[英]MySQL - Foreign key on delete cascade - Is there a defined execution order?
我在使用MySQL時遇到問題-多個表上的CASCADE ON DELETE規則。 顯然,“ CASCADE ON DELETE”規則的執行順序取決於其定義順序。
但是這個執行順序是否定義明確或取決於MySQL版本?
這是我的三個表“ A”,“ B”,“ C”的簡單示例
create table `A` (`id` NUMERIC(10,0) NOT NULL) ENGINE=INNODB;
create table `B` (`id` NUMERIC(10,0) NOT NULL, `a_id` NUMERIC(10,0) NOT NULL) ENGINE=INNODB;
create table `C` (`id` NUMERIC(10,0) NOT NULL, `a_id` NUMERIC(10,0) NOT NULL, `b_id` NUMERIC(10,0) NOT NULL) ENGINE=INNODB;
ALTER TABLE `A` ADD PRIMARY KEY (`id`);
ALTER TABLE `B` ADD PRIMARY KEY (`id`);
ALTER TABLE `C` ADD PRIMARY KEY (`id`);
ALTER TABLE `C` ADD CONSTRAINT `C1` FOREIGN KEY (`a_id`) REFERENCES `A` (`id`) ON DELETE CASCADE;
ALTER TABLE `B` ADD CONSTRAINT `B1` FOREIGN KEY (`a_id`) REFERENCES `A` (`id`) ON DELETE CASCADE;
ALTER TABLE `C` ADD CONSTRAINT `C2` FOREIGN KEY (`b_id`) REFERENCES `B` (`id`);
如果我插入以下數據:
INSERT INTO A (id) VALUES (1);
INSERT INTO B (id, a_id) VALUES (1,1);
INSERT INTO C (id, a_id, b_id) VALUES (1,1,1);
...並嘗試刪除表“ A”中的唯一條目:
delete from A where id=1;
...我收到以下錯誤消息:
Cannot delete or update a parent row: a foreign key constraint fails (`C`, CONSTRAINT `C2` FOREIGN KEY (`b_id`) REFERENCES `B` (`id`))
但是,如果我將外鍵約束的定義更改為:
ALTER TABLE `C` ADD CONSTRAINT `C1` FOREIGN KEY (`a_id`) REFERENCES `A` (`id`) ON DELETE CASCADE;
ALTER TABLE `C` ADD CONSTRAINT `C2` FOREIGN KEY (`b_id`) REFERENCES `B` (`id`);
ALTER TABLE `B` ADD CONSTRAINT `B1` FOREIGN KEY (`a_id`) REFERENCES `A` (`id`) ON DELETE CASCADE;
...一切順利...
謝謝你的幫助
您的ALTER TABLE table ADD CONSTRAINT foreign_key FOREIGN KEY
相同,因此它們不能成為錯誤原因。
(...文本已刪除)
無法解釋這種奇怪的行為。 可以建議一種解決方法:
SET FOREIGN_KEY_CHECKS = 0;
DELETE FROM A WHERE ID=1;
SET FOREIGN_KEY_CHECKS = 1;
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.