Database Animations: What’s a Residual Predicate and Why Is It Bad?

This article by Brent Ozar explains residual predicates in SQL Server execution plans. It uses a query on the Stack Overflow Users table to show how filtering on a non-indexed column (Reputation) after an index seek on Location leads to unnecessary key lookups. The post illustrates the performance impact with animations and advises adding the column to the index's include list to avoid the extra reads. It also teaches how to identify residual predicates by hovering over the Key Lookup operator and looking for a plain 'Predicate' (not 'Seek Predicate'). This is a technical database performance tuning guide relevant to IT professionals.