Three-Valued Logic

SQL logic in which a condition can be true, false, or unknown.

What is Three-Valued Logic in a relational database?

Three-Valued Logic — SQL logic in which a condition can be true, false, or unknown.

SELECT customer_id
FROM customer
WHERE phone_number = NULL;
-- The comparison is UNKNOWN; use IS NULL instead.

Level: Master · More Database terms at this level

Updated September 27, 2026