MYSQL Tutorial

MySQL NOT NULL Constraint

The NOT NULL constraint ensures that a column cannot contain NULL values. Use it for fields that must always have meaningful data.

Syntax

column_name data_type NOT NULL
  

Defining NOT NULL in CREATE TABLE

CREATE TABLE users (
  user_id   INT AUTO_INCREMENT PRIMARY KEY,
  name      VARCHAR(100) NOT NULL,
  email     VARCHAR(150) NOT NULL,
  age       INT
);
  

Adding NOT NULL to Existing Column

ALTER TABLE users
MODIFY COLUMN age INT NOT NULL;
  

Removing NOT NULL Constraint

ALTER TABLE users
MODIFY COLUMN email VARCHAR(150) NULL;
  

Common Use Cases

• Usernames, emails, or passwords that must always be provided.
• Order dates, product IDs, or any mandatory business fields.
• Foreign key columns when you require strict referential integrity.