|
uery OK, 0 rows affected (0.05 sec)
插入记录:
mysql> insert into country(country) values('china');
Query OK, 1 row affected (0.03 sec)
mysql> select * from country;
+------------+---------+
| country_id | country |
+------------+---------+
| 1 | china |
+------------+---------+
1 row in set (0.00 sec)
mysql> insert into city(country_id) values(1);
Query OK, 1 row affected (0.11 sec)
mysql> select * from city;
+---------+------------+
| city_id | country_id |
+---------+------------+
| 1 | 1 |
+---------+------------+
1 row in set (0.00 sec)
city表依赖country表的country_id字段，删除会出错:
mysql> delete from country where country_id=1;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constrai
nt fails (`tom1/city`, CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFER
ENCES `country` (`country_id`) ON UPDATE CASCADE)
现在更新country表中的country_id字段，city表的country_id字段也会被同步更新，这是因为在创建city表的最后加了:on update cascade，即:更新时做级联操作
mysql> update country set country_id=1000 where country_id=1;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from city;
+---------+------------+
| city_id | country_id |
+---------+------------+
| 1 | 1000 |
+---------+------------+
1 row in set (0.00 sec)
|