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SQL NOT NULL Keyword

NOT NULL

The NOT NULL constraint enforces a column to not accept NULL values, which means that you cannot insert or update a record without adding a value to this field.

The following SQL ensures that the "ID", "LastName", and "FirstName" columns will NOT accept NULL values:

Example

CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int
);

The following SQL creates a NOT NULL constraint on the "Age" column when the "Persons" table is already created:

ALTER TABLE Persons
MODIFY Age int NOT NULL;

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