1.在创建表格时就设置主键和外键

CREATE table employee2(

EmpId VARCHAR(10)    PRIMARY KEY,

EmpName VARCHAR(20),

EmpPassword VARCHAR(32),

Gender VARCHAR(2),

BirthDate date,

EmpPic VARCHAR(50),

DeptId INT,

FOREIGN KEY (DeptId) REFERENCES Dept2 (DeptId)

)

1.在创建表格结束设置主键和外键

--设置主键

ALTER TABLE employee3 ADD PRIMARY KEY(EmpId)

--设置外键

ALTER TABLE employee3 ADD FOREIGN KEY(DeptId) REFERENCES Dept(DeptId)