Mysql 为什么我不能在上面形成外键?
我正在尝试将外键从department表添加到employee表。第一个已完成,但我无法创建部门表,它会弹出错误 错误1005 HY000:无法创建表'assignment'。'department'errno:150外键约束格式不正确 像这样Mysql 为什么我不能在上面形成外键?,mysql,sql,foreign-keys,Mysql,Sql,Foreign Keys,我正在尝试将外键从department表添加到employee表。第一个已完成,但我无法创建部门表,它会弹出错误 错误1005 HY000:无法创建表'assignment'。'department'errno:150外键约束格式不正确 像这样 CREATE TABLE employee ( First_Name VARCHAR(15) NOT NULL, Mid_Name CHAR, Last_Name VARCHAR(15) NOT NULL, SSN_Num
CREATE TABLE employee
(
First_Name VARCHAR(15) NOT NULL,
Mid_Name CHAR,
Last_Name VARCHAR(15) NOT NULL,
SSN_Number CHAR(9) PRIMARY KEY NOT NULL,
Birthday DATE,
Address VARCHAR(50),
Sex CHAR CHECK(Sex='M' OR Sex='F' OR Sex='m' OR Sex='f'),
Salary Decimal(10,2) DEFAULT'800',
Supervisor_SSN CHAR(9),
Department_Number INT,
CONSTRAINT fk_employee FOREIGN KEY(Supervisor_SSN)
REFERENCES employee(SSN_Number) ON DELETE SET NULL
);
CREATE TABLE department
(
Department_Name VARCHAR(15) NOT NULL UNIQUE,
Department_Number INT PRIMARY KEY NOT NULL,
Manaager_SSN CHAR(9) NOT NULL,
Manager_Start_Date Date,
CONSTRAINT fk_manager FOREIGN KEY(Manaager_SSN)
REFERENCES employee(SSN_Number) ON DELETE SET NULL
);
我希望将管理器SSN上的外键添加到employee表中的SSN编号。如果列声明为非空,则DELETE SET NULL上的选项无效。您告诉它将列设置为不可能的值
因此,要么将manager_SSN的声明更改为NULL,要么将外键更改为ON DELETE CASCADE。前者可能更合适——如果部门经理离开公司,通常不会解散该部门。外键定义包括
... ON DELETE SET NULL
^^^^^^^^
但是外键列被定义为非NULL
Manaager_SSN CHAR(9) NOT NULL,
^^^^^^^^
这真的很有帮助,谢谢!谢谢你!这真的很有帮助!