Why Your SQL Is Slower Than It Should Be

Slow SQL queries are rarely caused by hardware or the database engine itself. Three main culprits are identified: poor query design (e.g., correlated subqueries, inefficient joins that don't scale), missing indexes (forcing full table scans as data grows), and poor database design (e.g., Entity-Attribute-Value models that become bottlenecks at scale). Solutions include rewriting queries using joins, subqueries, CTEs, or window functions; adding indexes on WHERE clauses, join conditions, and sort columns; and redesigning problematic schema patterns through denormalization or targeted structural changes.