Why Database Indexes Fail Without Column Ordering

Episode 106 of Database Tech with Fexingo dives into a subtle but devastating performance trap: multi-column indexes with the wrong column order. Lucas and Luna walk through a real-world example from an e-commerce database where a well-intentioned index on (status, created_at) caused queries to scan millions of rows instead of hundreds. They explain how B-tree index traversal works, why equality columns must come first, and how range predicates like date comparisons kill index efficiency when placed after a low-selectivity column. The episode also covers the difference between filter and access predicates, and why understanding selectivity is more important than indexing every column. A concrete, actionable lesson for anyone tuning SQL databases — from Postgres to MySQL to SQL Server. #DatabaseIndexes #SQLPerformance #MultiColumnIndex #ColumnOrdering #BTreeIndex #QueryOptimization #Selectivity #IndexDesign #DatabaseTuning #Postgres #MySQL #SQLServer #IndexingStrategy #QueryPlan #RangePredicate #DatabaseTech #FexingoBusiness #BusinessPodcast Keep every episode free: buymeacoffee.com/fexingo