Question

我无法弄清楚为什么这不是编译它与外键有某种关系：

Drop Table Employee;
Drop Table Department;


Create Table Employee(
EmpNr int not null primary key,
EmpName Varchar(35) not null,
Dept Varchar (2) not null,
Gender char not null
);

Create Table Department(
DeptCode Varchar (2) not null primary key,
DeptName Varchar (35) not null,
Foreign Key (DeptCode) references Employee (Dept)
);

insert into Employee values (001, 'HagarT','DV','M'),
                               (002, 'WongS','DV','F'),
                               (003, 'Jones','MK','F'), 
                               (004, 'MifuneK','SL','M');

insert into Department values ('DV',  'Development'), 
                                 ('MK', 'Marketing'), 
                                 ('RS',  'Research'),                               
                                 ('SL', 'Sales');

Answer 1

您需要Dept PRIMARY KEY或UNIQUE作为FK

Create Table Employee(
    EmpNr int not null primary key,
    EmpName Varchar(35) not null,
    Dept Varchar (2) unique not null,
    Gender char not null
);

正如您所看到的，Employee有两行'DV'，因此对于Department来说是陌生的？

我想你想要的是

Create Table Employee(
    EmpNr int not null primary key,
    EmpName Varchar(35) not null,
    Dept Varchar (2) not null,
    Gender char not null,
    Foreign Key (Dept) references Department (DeptCode)
);

外键问题SQL

1 个答案: