Java Tech Enthusiast

Oct 4, 2026 · Databases

Why SQL NULL Can't Use Equals: Three-Valued Logic & Hidden Pitfalls

This article explains why SQL NULL represents an unknown state rather than a value, how three-valued logic (TRUE, FALSE, UNKNOWN) breaks equality comparisons, and demonstrates practical pitfalls with WHERE clauses, NOT IN subqueries, aggregate functions, and MySQL's NULL-safe operator.