Apologies if this is duplication; the closest existing question I could find was this which touches on the subject but does not resolve it.
I was wondering what is the cause and possible solution to the situation which I have seen many times whereby when browsing 'unanswered questions', the answer has already been given in the comments. This appears to be discouraged (I'm relatively new here) but it's not clear what can be done to combat it. At the very least, if no actual answers are posted (or none which resolve the query to the same level as that definitive comment), it doesn't seem possible for the question to ever be marked as answered, even if the asker and other visitors can upvote the comment in question (no pun intended).
Is this a common issue, and can anything be done about it? Is there a flag I'm unfamiliar with?