这应该没有问题。考虑以下示例：
CREATE TABLE table2 ( id int PRIMARY KEY, name varchar(20)) ENGINE=INNODB;CREATE TABLE table1 ( id int PRIMARY KEY, t2_id int, FOREIGN KEY (t2_id) REFERENCES table2 (id)) ENGINE=INNODB;INSERT INTO table2 VALUES (1, 'First Row');INSERT INTO table2 VALUES (2, 'Second Row');INSERT INTO table1 VALUES (1, 1);INSERT INTO table1 VALUES (2, 1);INSERT INTO table1 VALUES (3, 1);INSERT INTO table1 VALUES (4, 2);
这些表现在包含：
SELECt * FROM table1;+----+-------+| id | t2_id |+----+-------+| 1 | 1 || 2 | 1 || 3 | 1 || 4 | 2 |+----+-------+4 rows in set (0.00 sec)SELECt * FROM table2;+----+------------+| id | name |+----+------------+| 1 | First Row || 2 | Second Row |+----+------------+2 rows in set (0.00 sec)
现在我们可以成功删除这样的行：
DELETe FROM table1 WHERe id = 1;Query OK, 1 row affected (0.00 sec)DELETe FROM table1 WHERe t2_id = 2;Query OK, 1 row affected (0.00 sec)
但是，我们将无法删除以下内容：
DELETe FROM table2 WHERe id = 1;ERROR 1451 (23000): A foreign key constraint fails
如果我们
table1使用
CASCADE选项定义了外键，那么我们将能够删除父项，并且所有子项都将被自动删除：
CREATE TABLE table2 ( id int PRIMARY KEY, name varchar(20)) ENGINE=INNODB;CREATE TABLE table1 ( id int PRIMARY KEY, t2_id int, FOREIGN KEY (t2_id) REFERENCES table2 (id) ON DELETe CASCADE) ENGINE=INNODB;INSERT INTO table2 VALUES (1, 'First Row');INSERT INTO table2 VALUES (2, 'Second Row');INSERT INTO table1 VALUES (1, 1);INSERT INTO table1 VALUES (2, 1);INSERT INTO table1 VALUES (3, 1);INSERT INTO table1 VALUES (4, 2);
如果我们要重复之前失败的操作
DELETE，
table1则将删除其中的子行以及其中的父行
table2：
DELETE FROM table2 WHERe id = 1;Query OK, 1 row affected (0.00 sec)SELECt * FROM table1;+----+-------+| id | t2_id |+----+-------+| 4 | 2 |+----+-------+1 row in set (0.00 sec)SELECt * FROM table2;+----+------------+| id | name |+----+------------+| 2 | Second Row |+----+------------+1 row in set (0.00 sec)
