Django ORM

Efficient Ops

Aug 27, 2019 · Databases

Why MySQL Scans the Whole Table Before a Subquery? A Deep Dive into Slow Queries

This article investigates a MySQL slow query caused by a subquery that triggers a full‑table scan, explains MySQL's query rewrite behavior, and shows how Django's lazy ORM evaluation can worsen performance, offering practical fixes using explicit query execution or join rewrites.