How do you find records where phone is not provided (NULL) in customers?

• A. SELECT * FROM customers WHERE phone IS NULL;
• B. SELECT * FROM customers WHERE phone IS NOT NULL;
• C. SELECT * FROM customers WHERE phone = NULL;
• D. SELECT * FROM customers WHERE phone IS NOT NULL;

Answer: (A)

Null values represent missing or unknown data, so you can’t use the equals operator to test them. To find records where the phone field has no value, you must check for NULL with IS NULL. This condition is true only for rows where phone has no entry. Using IS NOT NULL would return rows where a phone number exists, not the missing ones. The approach using = NULL isn’t valid in SQL and will not match any rows. So the correct query is: SELECT * FROM customers WHERE phone IS NULL;