Mysql on delete cascade 总结

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建立测试表

查看版本信息

select version();
5.7.22

创建父表

drop table if exists Models;
CREATE TABLE Models
  (
    ModelID SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
   Name VARCHAR(40) NOT NULL,
    PRIMARY KEY (ModelID)
);

创建子表

drop table if exists Orders;
CREATE TABLE Orders
  (
    ID          SMALLINT UNSIGNED NOT NULL PRIMARY KEY,
   ModelID     SMALLINT UNSIGNED NOT NULL,
     Description VARCHAR(40),
    FOREIGN KEY (ModelID) REFERENCES Models (ModelID)
      ON DELETE cascade
  );

测试

测试用例-无父表相应数据，先插入子表

insert into Orders(Id,ModelID,Description) values (1,1,'a');

结果：执行失败
异常：[2018-07-31 11:08:01] 23000 Cannot add or update a child row: a foreign key constraint fails (

bov

.

Orders

, CONSTRAINT

Orders_ibfk_1

FOREIGN KEY (

ModelID

) REFERENCES

Models

(

ModelID

) ON DELETE CASCADE)
原因：通不过on delete cascade 的外键约束检查

测试用例-先插入主表数据，再插入子表数据

insert into Models(ModelID,Name) values (1,'a');
insert into Orders(Id,ModelID,Description) values (1,1,'a');

结果：执行成功

select * from Models;
1    a

select * from Orders;
1    1    a

测试用例-父子表都有数据，删除子表数据

delete from Orders where id = 1;

结果：执行成功

select * from Models;
1    a
select * from Orders;
为空

测试用例-父子表都有数据，删除父表书库

delete from Models where ModelID = 1;

结果：执行成功

select * from Models;
为空
select * from Orders;
为空

测试用例-父子表都有数据，更新子表外键

update Orders set ModelID = 3 where ID =1;

结果：执行失败
异常：[2018-07-31 12:33:02] 23000 Cannot add or update a child row: a foreign key constraint fails (

bov

.

Orders

, CONSTRAINT

Orders_ibfk_1

FOREIGN KEY (

ModelID

) REFERENCES

Models

(

ModelID

) ON DELETE CASCADE)
原因：通不过on delete cascade 的外键约束检查

测试用例-父子表都有数据，更新父表主键

update Models set ModelID = 2 where ModelID =1;

结果：执行失败
异常：[2018-07-31 12:34:24] 23000 Cannot delete or update a parent row: a foreign key constraint fails (

bov

.

Orders

, CONSTRAINT

Orders_ibfk_1

FOREIGN KEY (

ModelID

) REFERENCES

Models

(

ModelID

) ON DELETE CASCADE)
原因：通不过on delete cascade 的外键约束检查

测试用例-父子表都有数据，更新子表非外键

update Orders set Description = 'b' where ID =1;

结果：执行成功

select * from Orders;
1    1    b

测试用例-父子表都有数据，更新父表非主键

update Models set Name = 'c' where ModelID =1;

结果：执行成功

select * from Models;
1    c

今天带大家了解了MySQL的相关知识，希望对你有所帮助；关于数据库的技术知识我们会一点点深入介绍，欢迎大家关注golang学习网公众号，一起学习编程~