NOT NULL in SQL

The NOT NULL in SQL ensures that a column cannot have a NULL value. It mandates that every row must have a value for that column, preventing the insertion or updating of records with missing data in that column. This constraint is crucial for maintaining data integrity and ensuring that important fields are always populated with valid data. It can be defined during the creation of a table or added to an existing table. If an attempt is made to insert or update a row with a NULL value in a NOT NULL column, the database will reject the operation and return an error.