MySQL NOT NULL Constraint: Definition, Syntax, and Examples

The NOT NULL constraint in MySQL ensures that a column cannot store NULL values. It is used when you want to ensure that a column always contains a value and cannot be left empty.

NOT NULL on CREATE TABLE

Syntax:

CREATE TABLE table_name (
  column1 data_type NOT NULL,
  column2 data_type,
  column3 data_type NOT NULL
);

Example

CREATE TABLE students (

student_id INT PRIMARY KEY,

name VARCHAR(50) NOT NULL,

email VARCHAR(100),

age INT NOT NULL

);

Explanation:

name and age cannot be NULL.
email can accept NULL values.

NOT NULL on ALTER TABLE

Syntax:

ALTER TABLE table_name
MODIFY column_name data_type NOT NULL;

Example:

Example

ALTER TABLE students

MODIFY email VARCHAR(100) NOT NULL;

Explanation:

This makes the email column mandatory, ensuring it cannot store NULL values.

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