外键约束SQL

Question

继续收到错误无法添加外键约束，任何想法可能是noob错误，但我是SQL新手。

CREATE TABLE tblDept (

    Dept VARCHAR(50), 
    Name VARCHAR(50) 
); 

CREATE TABLE tblPersonnel (

    PersID INT PRIMARY KEY, 
    FullName VARCHAR(100), 
    Address VARCHAR(100), 
    Dept VARCHAR(50), 
    Grade VARCHAR (2), 
    Salary INT, 
    DateOfBirth DATE, 
    Manager INT, 
    FOREIGN KEY(Dept) REFERENCES tblDept(Dept) 

); 

CREATE TABLE PersonnelPhone (

    PersID INT, 
    Extension INT, 
    FOREIGN KEY (PersID) REFERENCES tblPersonnel(PersID) 
    ); 

CREATE TABLE tblPhone (
    Extension INT, 
    DeviceType VARCHAR, 
    VoiceMail BOOLEAN, 
    FOREIGN KEY (Extension) REFERENCES tblPersonnelPhone(Extension) 
    ); 

Answer 1

Extension在第二个表必须是PRIMARY KEY。

您可能想要实现多对多的关系。在这种情况下，Extension在PersonnelPhone应该是FOREIGN KEY和Extension在tblPhone应该是PRIMARY KEY。

Answer 2

那里有几个错误。这里有一个工作模式定义：

CREATE TABLE tblDept (
    Dept VARCHAR(50) PRIMARY KEY, 
    Name VARCHAR(50) 
); 

CREATE TABLE tblPersonnel (
    PersID INT PRIMARY KEY, 
    FullName VARCHAR(100), 
    Address VARCHAR(100), 
    Dept VARCHAR(50), 
    Grade VARCHAR(2), 
    Salary INT, 
    DateOfBirth DATE, 
    Manager INT, 
    FOREIGN KEY(Dept) REFERENCES tblDept(Dept) 
); 

CREATE TABLE tblPersonnelPhone (
    PersID INT, 
    Extension INT PRIMARY KEY, 
    FOREIGN KEY (PersID) REFERENCES tblPersonnel(PersID) 
); 

CREATE TABLE tblPhone (
    Extension INT, 
    DeviceType VARCHAR(100), 
    VoiceMail BOOLEAN, 
    FOREIGN KEY (Extension) REFERENCES tblPersonnelPhone(Extension) 
); 

以供将来参考，使用SQLFiddle分享这些类型的问题：http://sqlfiddle.com/#!9/2ce29