No, question URLs are not stored anywhere in the database, they are always generated from the ID and title. You simply pass them into the qa_q_path function:
$url = qa_q_path($questionid, $title);
Or in your case above:
$url = qa_q_path($params['postid'], $params['title']);
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Jan 12, 2019: Q2A 1.8.3 released!