This question already has an answer here:
What's everyone's opinion on closing an older question as a duplicate of a newer one, if the newer one is clearly the better resource? I'm looking at a special case right now, where the two were posted by the same person; the newer was migrated to SU before a commenter pointed out it was a repost. Is it considered good practice to close the older as a duplicate of the newer?
More generally, is it ok to do that for separate questions posted by different people, if the older question went unanswered but the newer has a good answer?
(I should probably mention I saw this question, but I think this is separate)