How To Add NOT NULL Constraint in SQL Server

A NOT NULL constraint on a column does not allow to enter a NULL value. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.

By default, every column can hold a NULL value.

NOT NULL Constraint on CREATE TABLE

In the below table tblEmployee EmpID, EmpFirstName, EmpLastName column values are mandatory because of NOT NULL constraint.

The EmpID column is a PRIMARY KEY column which does not accept NULL values and EmpFirstName and EmpLastName has NOT NULL constraints, therefore these columns does not accept NULL values.

CREATE TABLE tblEmployee
(

EmpID INT PRIMARY KEY,
EmpFirstName NVARCHAR(20) NOT NULL,
EmpLastName NVARCHAR(20) NOT NULL,
EmpEmail NVARCHAR(20),
EmpPhone NVARCHAR(15),
EmpDeptID INT,
EmpSalary INT,
EmpJoiningDate DATETIME