?️ MySQL IS NULL & IS NOT NULL

? Quick Overview

In MySQL, the IS NULL and IS NOT NULL operators are used to test for NULL values. These checks are extremely important when working with databases from PHP applications.

? Key Concepts

• NULL represents missing or unknown data
• IS NULL checks for missing values
• IS NOT NULL checks for existing values
• = NULL does not work in SQL

? Syntax & Theory

// Basic syntax for checking NULL values
SELECT column1, column2
FROM table_name
WHERE column_name IS NULL;

? Using IS NULL

The IS NULL operator returns records where a column has no value.

// Fetch employees without department assigned
SELECT * FROM employees
WHERE department IS NULL;

✨ Using IS NOT NULL

The IS NOT NULL operator filters rows where a value exists.

// Fetch employees who have a department
SELECT * FROM employees
WHERE department IS NOT NULL;

? Combining Conditions

You can combine both operators using logical conditions.

// Demonstration of combined NULL checks
SELECT * FROM employees
WHERE department IS NULL OR department IS NOT NULL;

? Live Output / Explanation

The above queries return rows depending on whether the column contains missing or existing data. This is commonly used in PHP-based filters and validations.

? Interactive Concept

Imagine a PHP form where optional fields like phone number are left empty. These values are stored as NULL and checked using IS NULL during reports.

? Use Cases

• Finding users who skipped optional fields
• Checking incomplete records
• Validating database entries in PHP applications