mysql怎么设置级联删除

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。

alter table B add constraint fk_ID foreign key (ID) references A(ID) on delete cascade

这样只需：delete from A where ID=nnnn就可以自动删除对应B表内容了。

通过外键无法实现同步更新。