Related knowledge about SQL NOT NULL constraints

SQL NOT NULL constraints are very important in PHP. This article will explain its related knowledge.

SQL NOT NULL Constraints

NOT NULL constraints force columns not to accept NULL values.

NOT NULL constraint forces the field to always contain a value. This means that you cannot insert a new record or update a record without adding a value to the field.

The following SQL statement forces the "Id_P" column and the "LastName" column not to accept NULL values:

CREATE TABLE Persons
(
Id_P int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)

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