首先，目前在產(chǎn)品環(huán)境可用的MySQL版本（指4.0.x和4.1.x）中，只有InnoDB引擎才允許使用外鍵，所以，我們的數(shù)據(jù)表必須使用InnoDB引擎。
下面，我們先創(chuàng)建以下測試用數(shù)據(jù)庫表：
CREATE TABLE `roottb` (
`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,
`data` VARCHAR(100) NOT NULL DEFAULT '',
PRIMARY KEY (`id`)
) TYPE=InnoDB;
CREATE TABLE `subtb` (
`id` INT(11) UNSIGNED AUTO_INCREMENT NOT NULL,
`rootid` INT(11) UNSIGNED NOT NULL DEFAULT '0',
`data` VARCHAR(100) NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
INDEX (`rootid`),
FOREIGN KEY (`rootid`) REFERENCES roottb(`id`) ON DELETE CASCADE
) TYPE=InnoDB;
注意：
1、必須使用InnoDB引擎；
2、外鍵必須建立索引（INDEX）；
3、外鍵綁定關(guān)系這里使用了“ ON DELETE CASCADE”，意思是如果外鍵對(duì)應(yīng)數(shù)據(jù)被刪除，將關(guān)聯(lián)數(shù)據(jù)完全刪除，更多信息請(qǐng)參考MySQL手冊(cè)中關(guān)于InnoDB的文檔；
好，接著我們?cè)賮聿迦霚y試數(shù)據(jù)：
INSERT INTO `roottb` (`id`,`data`)
VALUES ('1', 'test root line 1'),
('2', 'test root line 2'),
('3', 'test root line 3');
INSERT INTO `subtb` (`id`,`rootid`,`data`)
VALUES ('1', '1', 'test sub line 1 for root 1'),
('2', '1', 'test sub line 2 for root 1'),
('3', '1', 'test sub line 3 for root 1'),
('4', '2', 'test sub line 1 for root 2'),
('5', '2', 'test sub line 2 for root 2'),
('6', '2', 'test sub line 3 for root 2'),
('7', '3', 'test sub line 1 for root 3'),
('8', '3', 'test sub line 2 for root 3'),
('9', '3', 'test sub line 3 for root 3');
我們先看一下當(dāng)前數(shù)據(jù)表的狀態(tài)：
mysql>; show tables;
+----------------+
| Tables_in_test |
+----------------+
| roottb |
| subtb |
+----------------+
2 rows in set (0.00 sec)
mysql>; select * from `roottb`;
+----+------------------+
| id | data |
+----+------------------+
| 1 | test root line 1 |
| 2 | test root line 2 |
| 3 | test root line 3 |
+----+------------------+
3 rows in set (0.05 sec)
mysql>; select * from `subtb`;
+----+--------+----------------------------+
| id | rootid | data |
+----+--------+----------------------------+
| 1 | 1 | test sub line 1 for root 1 |
| 2 | 1 | test sub line 2 for root 1 |
| 3 | 1 | test sub line 3 for root 1 |
| 4 | 2 | test sub line 1 for root 2 |
| 5 | 2 | test sub line 2 for root 2 |
| 6 | 2 | test sub line 3 for root 2 |
| 7 | 3 | test sub line 1 for root 3 |
| 8 | 3 | test sub line 2 for root 3 |
| 9 | 3 | test sub line 3 for root 3 |
+----+--------+----------------------------+
9 rows in set (0.01 sec)
嗯，一切都正常，好，下面我們要試驗(yàn)我們的級(jí)聯(lián)刪除功能了。
我們將只刪除roottb表中id為2的數(shù)據(jù)記錄，看看subtb表中rootid為2的相關(guān)子紀(jì)錄是否會(huì)自動(dòng)刪除：
mysql>; delete from `roottb` where `id`='2';
Query OK, 1 row affected (0.03 sec)
mysql>; select * from `roottb`;
+----+------------------+
| id | data |
+----+------------------+
| 1 | test root line 1 |
| 3 | test root line 3 |
+----+------------------+
2 rows in set (0.00 sec)
mysql>; select * from `subtb`;
+----+--------+----------------------------+
| id | rootid | data |
+----+--------+----------------------------+
| 1 | 1 | test sub line 1 for root 1 |
| 2 | 1 | test sub line 2 for root 1 |
| 3 | 1 | test sub line 3 for root 1 |
| 7 | 3 | test sub line 1 for root 3 |
| 8 | 3 | test sub line 2 for root 3 |
| 9 | 3 | test sub line 3 for root 3 |
+----+--------+----------------------------+
6 rows in set (0.01 sec)
嗯，看subtb表中對(duì)應(yīng)數(shù)據(jù)確實(shí)自動(dòng)刪除了，測試成功。
結(jié)論：在MySQL中利用外鍵實(shí)現(xiàn)級(jí)聯(lián)刪除成功！
-----------轉(zhuǎn)帖:http://www.chinaunix.net/jh/17/462977.html
posted on 2008-04-07 12:00
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