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SQL NOT NULL constraint

In case of default, a table column accepts NULL values.

SQL NOT NULL constraint

NOT NULL constraints forced the column does not accept NULL values.

NOT NULL constraint mandatory field always contains a value. This means that if you do not add value to a field, you can not insert a new record or update the record.

The following SQL mandatory "P_Id" column and the "LastName" column does not accept NULL values:

P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)