mysql怎么设置级联删除

这个在建表的时候就可以指定了

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。

举例：

1、建筑表

CREATE

TABLE

buildings

(

building_no

INT

PRIMARY

KEY

AUTO_INCREMENT,

building_name

VARCHAR(255)

NOT

NULL,

address

VARCHAR(255)

NOT

NULL

)

2、房间表

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

//这里指定了级联删除

)

3、执行删除会把building_no=2的room记录都删除了

DELETE

FROM

buildings

WHERE

building_no

=

2

设定外键为级联删除就可以了。

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。

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