Avoid wrapping indexed columns in functions so the optimizer can use the index.
A function on an indexed column disables the index, forcing a full scan even when one exists.
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Applying a function to an indexed column (e.g. DATE(col), UPPER(col)) makes the predicate non-sargable: MySQL must evaluate the function per row and cannot use the index. Rewrite to compare the bare column against a computed bound.
-- Bad: function on column disables the index
SELECT * FROM events WHERE DATE(created_at) = '2026-06-01';
-- Good: range on the raw column uses the index
SELECT * FROM events
WHERE created_at >= '2026-06-01'
AND created_at < '2026-06-02';