SQL NOT NULL

SQL NOT NULL: The NOT NULL constraint enforces a column to NOT accept NULL values. This means a column with not null always needs to have a value. This means that you cannot insert a new record, or update a record without adding a value to this field

Example:

CREATE TABLE employee
(
     Emp_id int NOT NULL,
     LastName varchar(255) NOT NULL,   
     FirstName varchar(255),
     Address varchar(255),
     City varchar(255)
)