Re: 5.5: UPDATE massively slower than SELECT. Both affect zero rows.

[Rick James]

UPDATE and SELECT sometimes use different optimizers; I don't know if this is such a case.

This might take advantage of SELECT's speed:
UPDATE products AS p
JOIN
( SELECT v.upc
FROM upcLike AS v
INNER JOIN batchList as l
ON l.upc = concat('LC',convert(v.likecode, char))
INNER JOIN batches AS b ON b.batchID = l.batchID
WHERE l.upc LIKE 'LC%'
AND l.batchID = 4895
) AS x USING (upc)
SET p.modified = NOW();

`batchList` needs a composite index:
INDEX(batchID, upc)