Handling NULL Values

NULL represents missing or unknown data. It's not the same as 0, empty string, or "nothing" — it means the value is unknown.

⚠️ The #1 Mistake with NULL

You cannot use = to check for NULL!

-- ❌ WRONG - This will NEVER find NULL values!
SELECT * FROM customers WHERE email = NULL;
-- ✅ CORRECT
SELECT * FROM customers WHERE email IS NULL;
-- ✅ Find rows where email exists
SELECT * FROM customers WHERE email IS NOT NULL;

Why Can't You Use = NULL?

In SQL, NULL means "unknown". Comparing anything to an unknown value is also unknown — so NULL = NULL returns FALSE, not TRUE!

Real-World Examples of NULL

• Customer without a phone number
• Order without a shipping date (not yet shipped)
• Product without a description

Your Task

Find all customers who have not provided an email address.