MySQL IS NOT NULL Operator

Introduction

In this chapter, we will learn about the IS NOT NULL operator in MySQL. The IS NOT NULL operator is used to filter records that do not have NULL values in a specified column. NULL represents a missing or undefined value in a database. By using IS NOT NULL, you can ensure that your queries return only rows where the column has a valid value. We will cover the syntax, examples, and important considerations for using the IS NOT NULL operator.

Syntax

The basic syntax for the IS NOT NULL operator is:

SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NOT NULL;

• column_name: The column to check for non-NULL values.

Using IS NOT NULL Operator

Example with SELECT

SELECT first_name, last_name, email
FROM students
WHERE email IS NOT NULL;

This example retrieves rows where the email column does not have NULL values.

Example with UPDATE

UPDATE students
SET email = '[email protected]'
WHERE email IS NOT NULL;

This example updates the email column to ‘[email protected]’ for rows where the email column does not have NULL values.

Example with DELETE

DELETE FROM students
WHERE email IS NOT NULL;

This example deletes rows where the email column does not have NULL values.

Full Example

Let’s go through a full example where we create a table, insert data into it, and use the IS NOT NULL operator to filter records.

1. Create a Database:

CREATE DATABASE school;

2. Select the Database:

USE school;

3. Create a Table:

CREATE TABLE students (
    id INT PRIMARY KEY AUTO_INCREMENT,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL,
    email VARCHAR(100),
    enrollment_date DATE
);

4. Insert Data into the Table:

INSERT INTO students (first_name, last_name, email, enrollment_date) VALUES
('Rahul', 'Sharma', '[email protected]', '2023-07-01'),
('Priya', 'Singh', NULL, '2023-07-02'),
('Amit', 'Kumar', '[email protected]', '2023-07-03'),
('Neha', 'Verma', NULL, '2023-07-04'),
('Sahil', 'Mehta', '[email protected]', '2023-07-05');

5. Use the IS NOT NULL Operator with SELECT:

SELECT first_name, last_name, email
FROM students
WHERE email IS NOT NULL;

Output

6. Use the IS NOT NULL Operator with UPDATE:

UPDATE students
SET email = '[email protected]'
WHERE email IS NOT NULL;

7. Verify the Update:

SELECT first_name, last_name, email
FROM students
WHERE email = '[email protected]';

Output

8. Use the IS NOT NULL Operator with DELETE:

DELETE FROM students
WHERE email IS NOT NULL;

9. Verify the Deletion:

SELECT first_name, last_name, email
FROM students
WHERE email IS NOT NULL;

Output

(empty result set)

Important Considerations

• NULL Values: NULL is not the same as an empty string or zero. It represents an unknown or missing value.
• Comparison with NULL: You cannot use regular comparison operators like = or <> to check for NULL values. Always use IS NULL or IS NOT NULL for such checks.
• Performance: Checking for NULL or non-NULL values can impact performance, especially on large datasets. Ensure appropriate indexing and optimize queries to improve performance.

Conclusion

The IS NOT NULL operator is used for filtering data based on non-NULL values in MySQL queries. This chapter covered how to use the IS NOT NULL operator with SELECT, UPDATE, and DELETE statements, provided examples, and discussed important considerations.