13518219792
这个在建表的时候就可以指定了
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CREATE TABLE buildings (
building_no INT PRIMARY KEY AUTO_INCREMENT,
building_name VARCHAR(255) NOT NULL,
address VARCHAR(255) NOT NULL
);
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
);
当执行
DELETE FROM buildings
WHERE
building_no = 2;的时候，rooms表中的building_no =2的记录都会被删掉。
CONSTRAINT `外键名` FOREIGN KEY (`外键的字段`) REFERENCES `外键关联的表` (`外键关联的字段`) ON DELETE CASCADE ON UPDATE CASCADE
ON DELETE代表删除时
ON UPDATE代表更新时
CASCADE代表级联
mysql:
1、先给B表添加主键列
alter table tableB add constraint b_PK primary key(date,channel);
2、将B表的组合主键关联到A表的外键组合键中
alter table tableB add constraint tableB_fk foreign key(date,channel) references tableA (date,channel) on DELETE CASCADE ;
3 delete from tableA where date =? and channel =? 就出发相关记录··~
