How to add Primary key in the existing table in SQL server ?

Primary key is a kind of constraint in SQL server .To add the primary key in the existing table , you can do it in two ways.

1. Using SQL Management Studio
2. Using T-SQL Query

Using SQL Management Studio:

Step1:

Expand the database ,right click the required table and click the design option as shown below.

Step2:

Right click the required column and select the option as set the primary key as shown below.

Step3:

After clicking the option you can find the Key icon in the selected column as shown below.

Primary key is created successfully in StudentDetail table using SQL Management studio.

Using T-SQL Query:

Refer : http://jksqlserver.blogspot.ae/2015/09/how-to-create-primary-key-in-sql-server.html