The NOT NULL constraint enforces a column to NOT accept NULL values.

The NOT NULL constraint enforces a field to always contain a value. This means that you cannot insert a new record, or update a record without adding a value to this field.

The following SQL enforces the "U_Id" column and the "LastName" column to not accept NULL values:

CREATE TABLE Users 
( 
U_Id int NOT NULL,
LastName varchar(255) NOT NULL, 
FirstName varchar(255), 
Address varchar(255), 
City varchar(255) 
) 
--when we want insert null value lastname get error 
insert into Users(U_Id,LastName,FirstName,Address,City) 
 values(1011,null,'Ravi','mumbai','thane') 

When I insert lastname null get error.
Result :