SQL Foreign key Constraint

A Foreign key in one table points to a primary key in another table.

Firstly we create two tables:-

“employee” table: -

E_Id	Name	Address
1	Sachin	Kanpur
2	Amit	Aligarh
3	Sumt	Etah

“Emp” table

Emp_id	dept	E_Id
1	IT	2
2	sales	1

The SQL Foreign key constraint on create table

Create table Emp

(

Emp_id int NOT NULL PRIMARY KEY,

dept varchar (250) NOT NULL,

E_Id int Foreign Key references employee(E_Id)

)

SQL foreign Key constraint on ALTER Table

ALTER Table Emp

Add foreign key (E_Id)

References Employee (E_Id)

Drop a Foreign Key Constraint –

Alter table Emp

Drop contraint E_Id

                                                Author : - Sachin Pathak