SQL NOT NULL Constraint

SQL NOT NULL Constraint : SQL NOT NULL Constraint enforces a column to NOT accept NULL values.

  • By default, a column can hold NULL values.
  • The NOT NULL constraint enforces a column to NOT accept NULL values.
  • This enforces a field to always contain a value, which means that you cannot insert a new record, 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
);

 

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