Steps to create Primary Key in SQL Server

The PRIMARY KEY means unique and it identifies each record in a table uniquely. It must contain UNIQUE values and the value should not be NULL values. A table can have only one PRIMARY KEY .

PRIMARY KEY Diagram

PRIMARY KEY EXAMPLE:

    CREATE TABLE [dbo].[customer](
	    [CustomerID] int NOT NULL PRIMARY KEY,
	    [CustomerName] [varchar](50) NULL,
	    [CustomerLocation] [varchar](50) NULL,
	    [State] [varchar](50) NULL,
	    [City] [varchar](50) NULL,
	    [phoneno] [int] NULL,
	    [pincode] [int] NULL,
	    [Email] [varchar](100) NULL
)

                        

Create primary key on existing Table

Requirement: To create primary key on ID field of Students Table.

ALTER TABLE STUDENTS ADD PRIMARY KEY (ID)

HOW TO CREATE PRIMARY KEY ON MULTIPLE COLUMNS?

ALTER TABLE STUDENTS ADD CONSTRAINT PK_STUDENTS PRIMARY KEY(ID,STUDENTNAME)