Free Web Development Online Tutorials, Learn to Code
Primary Key Foreign key Relationship, Learn SQL Database Development, MS SQL Tutorial

Foreign key constraint Example in SQL Server

SQL FOREIGN KEY Constraint

A FOREIGN KEY in SQL is a key used to link two SQL tables together.

The table holding the foreign key reference is called the child table

Let’s look at the picture below
Here table "tbClassTeacherMap" is having a foreign key column called "TeacherId" , and the Foreign key Constraint name Is "FK_ tbClassTeacherMap_tbTeacher"


How to create foreign key in SQL

So far you have understood what is Foreign key column, and what is Foreign Key Constraint, Now you learn how to create Foreign Key Constraint.

You can create Foreign Key two ways
  • At the time of Table Creation
    CREATE TABLE ClassStudentMap (
    CSId	int not null identity(1,1)  PRIMARY KEY,
    ClassId int NOT NULL,
    StudentId bigint NOT NULL,
    CONSTRAINT FK_ClassStudentMap_Student FOREIGN KEY (StudentId)
    REFERENCES tbStudent(StudentId)
    );


  • Or you can Alter the Table
    alter TABLE ClassStudentMap add CONSTRAINT FK_ClassStudentMap_ClassRoom FOREIGN KEY (ClassId)
    REFERENCES tbClassRoom(crId)


Comment
Name
Email
Website
Subscribe
 
FOREIGN KEY Constraint in SQL Server

FOREIGN KEY Reference in SQL