See https://developer.atlassian.com/display/JIRADEV/Database+Schema#DatabaseSchema-Worklogs for the join part of the question.
My instincts sense another question behind this one though, with you mentioning jdbc? Could you tell us what your actual requirements are? Why you're asking this question?
I just saw you asked 33 questions so far. You haven't accepted a single answer as a correct one so far. Please do us all a favor and accept the answers as a correct one, which helped you or where you think they are correct.
please see also following discussion.
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