Home

Foreign Keys

   

Introduction

To create a foreign key in the SQL, the basic formula to use is:

FOREIGN KEY REFERENCES ParentTableName(ForeignKeyCcolumn) 

Here is an example:

CREATE TABLE Persons
(
    PersonID int identity(1,1) PRIMARY KEY NOT NULL,
    FirstName nvarchar(20),
    LastName nvarchar(20) NOT NULL,
    GenderID int NULL FOREIGN KEY REFERENCES Genders(GenderID)
);

A Constraint on a Foreign Key

To create a foreign key as a constraint, use the CONSTRAINT keyword followed by the desired name and continue the rest as we saw above. Her is an example:

CREATE TABLE Persons
(
    PersonID int identity(1,1) PRIMARY KEY NOT NULL,
    FirstName nvarchar(20),
    LastName nvarchar(20) NOT NULL,
    GenderID int NULL CONSTRAINT FKGenders
                       FOREIGN KEY REFERENCES Genders(GenderID)
);

Home Copyright © 2007-2011 FunctionX.com, Inc.