Three-valued logic

Learn how NULL behaves with AND, OR and comparisons.

IFNULL and NVL

IFNULL (MySQL) and NVL (Oracle) take two values; if the first is NULL they return the second. They are a short form of COALESCE.

SELECT IFNULL(phone, 'yok') AS tel FROM customers;

This query writes 'yok' when phone is null.

IFNULL(phone, 'yok') AS tel is selected from customers.

IFNULL takes only two values; for three or more fallbacks use COALESCE. PostgreSQL does not have IFNULL.

Select phone with 'none' fallback using IFNULL from customers.

Show example solution

SELECT IFNULL(phone, 'yok') AS tel
FROM customers

Fallback

SELECT ____(phone, 'yok') FROM customers;

Show answer

SELECT IFNULL(phone, 'yok') FROM customers;