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 date nobody writes down.
-- before reaching for this
ANALYZE TABLE orders; -- refresh the statistics
-- then, if it is genuinely needed
SELECT * FROM orders FORCE INDEX (idx_customer_status)
WHERE customer_id = 91 AND status = 'paid';Almost every case where a hint appears to help is stale statistics, and ANALYZE TABLE is the cheaper fix. Where a hint is genuinely warranted it belongs with a comment saying which query plan it is working around and on what date, because a hinted query does not adapt: the day the table grows past the point where a different index is better, it will still be using this one and nothing will report it.