liandk

Aug 23, 2026 · Databases

MySQL Covering Index & Back‑Table Optimization: Hands‑On Guide to Eliminate Lookups

The article explains why MySQL back‑table lookups (回表) double I/O and degrade performance, defines covering indexes that retrieve all needed columns from a secondary index, shows how to identify back‑table cases via EXPLAIN, and provides step‑by‑step commands to create, test, and verify covering indexes for high‑frequency queries.