Grade SMALLINT, PRIMARY KEY (Sno, Cno), /*在表级定义实体完整性*/ FOREIGN KEY (Sno) REFERENCES Student(Sno), /*在表级定义参照完整性*/ FOREIGN KEY (Cno) REFERENCES Course(Cno) /*在表级定义参照完整性*/ ); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. (...
IDvarchar(15) COMMENT'身份证号',CONSTRAINTuq_Person_IDUNIQUE(email,ID),CONSTRAINTpk_PersonID_NamePRIMARYkey(P_id,P_Name) );descPersons; 创建unique约束成功 4.外键约束(转自:http://c.biancheng.net/view/2441.html) MySQL外键约束(FOREIGN KEY)是表的一个特殊字段,经常与主键约束一起使用。对于两个...
add constraint fk_b_a foreign key (id_a) references a (id) on update cascade on delete cascade; 删除外键约束 alter table b drop foreign key fk_b_a; 外键的约束关系 父表: 被引用的表,column必须为primary key 子表: 引用主表,外键的某一column引用父表的primary key cascade: 在父表update/de...
However, MySQL does not enforce a requirement that the referenced columns be UNIQUE or be declared NOT NULL. A FOREIGN KEY constraint that references a non-UNIQUE key is not standard SQL but rather an InnoDB extension. The NDB storage engine, on the other hand, requires an explicit unique ...
CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) ); FOREIGN KEY on ALTER TABLETo create a FOREIGN KEY constraint on the "PersonID" column when the "Orders" table is already created, use the following SQL:ALTER TABLE Orders ADD FOREIGN KEY (PersonID) REFERENCES Pe...
我想在students表中创建外键ClassID,关联到class表中的主键ClassID上,要求级联更新删除,但创建外键过程中显示Cannot add foreign key constraint。 先看一下关联表结构, classes表结构 students表结构 出现该问题时要考虑一下几点: 1、两张表所用引擎是否一致 ...
Email VARCHAR(50) NOT NULL, Password_Hash TINYBLOB NOT NULL, Password_Salt TINYBLOB NOT NULL, Condicion TINYINT DEFAULT(1), FOREIGN KEY (Idrol) REFERENCES Role (Idrol) ); send me this error. the table Role exist and is int (11). any help please ...
ERROR 1062 (23000): Duplicate entry '10' for key 't_emp.PRIMARY' mysql> insert into t_emp values(11,'shenlulu','m'); Query OK, 1 row affected (0.04 sec) mysql> insert into t_emp values(null,'lili','m'); ERROR 1048 (23000): Column 'empno' cannot be null ...
Question is simple: why cannot I create this foreign key ? UPDATE 1: I tried replacing ON DELETE CASCADE with ON DELETE RESTRICT and nothing changes, also I tried to remove ON DELETE and ON UPDATE an nothing changes mysql sql foreign-keys foreign-key-relationship Share Improve this question ...
引言:MySQL中经常会需要创建父子表之间的约束,这个约束是需要建立在主外键基础之上的,这里解决了一个在创建主外键约束过程中碰到的一个问题。 1. 问题的提出 创建两个表: product: 商品表 sealer: 供货商表 相应的SQL如下: product: 代码语言:javascript ...