NOT NULL

SQL NOT NULL Keyword

The NOT NULL constraint ensures that a column cannot have a NULL value. This means that the column must always contain a value when a record is inserted or updated.

SQL NOT NULL Syntax

CREATE TABLE table_name (
    column1 datatype NOT NULL,
    column2 datatype,
    ...
);

CREATE TABLE table_name (

    column1 datatype NOT NULL,

    column2 datatype,

    ...

);

To add a NOT NULL constraint to an existing column in some databases:

ALTER TABLE table_name
MODIFY column_name datatype NOT NULL;

ALTER TABLE table_name

MODIFY column_name datatype NOT NULL;

Note: The MODIFY syntax may vary depending on the SQL engine.

SQL NOT NULL on CREATE TABLE Example

This query creates a new table DoctorsBackup where the first_name and last_name columns must have values.

CREATE TABLE DoctorsBackup (
    doctor_id INTEGER PRIMARY KEY,
    first_name TEXT NOT NULL,
    last_name TEXT NOT NULL
);

CREATE TABLE DoctorsBackup (

    doctor_id INTEGER PRIMARY KEY,

    first_name TEXT NOT NULL,

    last_name TEXT NOT NULL

);

SQL NOT NULL on Existing Table Example

This query alters the Students table to ensure the email column cannot have NULL values.

-- Not supported in SQLite:
ALTER TABLE Students
MODIFY email TEXT NOT NULL;

-- Not supported in SQLite:

ALTER TABLE Students

MODIFY email TEXT NOT NULL;

Note: This example does not work in our TechKubo playground (SQLite), because SQLite does not support modifying existing columns to add NOT NULL directly.

Tip: Always use NOT NULL on columns where a missing value would break your application logic or data integrity.

SQL NOT NULL Labs