강선우 “경찰, ‘1억 수수 인정하면 품격 지켜주겠다’ 압박”…경찰 “회유 없었다”

The article discusses the issue of redundant indexes in databases, specifically focusing on MySQL. It explains that a redundant index occurs when a single-column index is included in a composite index, which can be unnecessary as the single-column index can be used for lookups that the composite index can also satisfy. The article provides a method to identify and remove these redundant indexes using MySQL's standard view `sys.schema_redundant_indexes` or tools like `pt-duplicate-key-checker` and `sys.schema_unused_indexes`.

It also highlights the importance of not removing redundant indexes that are part of a foreign key constraint, as doing so can cause an error. The article concludes by demonstrating a safe way to drop a redundant index using ActiveRecord migration.