FORCE INDEX makes the immediate problem go away and freezes a decision the optimiser would otherwise revisit as the data changes. It is a fix with an expiry…
Finding the nearest branch used to mean a bounding-box query in SQL with a Haversine formula in the ORDER BY, which cannot use an index and gets slower…
LIKE cannot use an index and everyone knows it. The mapping, the analyzers that decide what matching means, the indexing pipeline, and the drift it introduces.
A JSON column cannot be indexed directly, so a query filtering on something inside it scans the table. A generated column extracts the value into a real column…
Five filters over 30,000 variations, and a request that never returns. Replacing EAV meta joins with a denormalised index table kept in sync by product hooks.