Query Optimization

SQL DISTINCT vs GROUP BY: When Each One Silently Lies to You

DISTINCT and GROUP BY often appear to produce identical results, leading many developers to use them interchangeably. However, they solve different problems, and misunderstanding their behavior can produce incorrect reports, hidden duplicates, misleading aggregations, and poor query performance.

Jul 21, 2026 5m read 👁 0

SQL NULL Comparisons Returning Wrong Results: IS NULL vs = NULL Traps

One of the most common SQL mistakes is comparing NULL values using = NULL instead of IS NULL. The result is queries that silently return incorrect or empty result sets. Learn why SQL treats NULL differently, understand three-valued logic, and write reliable queries that correctly handle missing data

Jul 01, 2026 4m read 👁 2