def get_comment_number(self, cdate):
        ts = to_utimestamp(cdate)
        for cnum, in self.env.db_query("""\
                SELECT oldvalue FROM ticket_change
                WHERE ticket=%s AND time=%s AND field='comment'
                """, (self.id, ts)):
            try:
                return int(cnum.rsplit('.', 1)[-1])
            except ValueError:
                break
Return the header row for the given table. E.g.::
dataset/ETHPy150Open edgewall/trac/trac/ticket/model.py/Ticket.get_comment_number--crossover with--dataset/ETHPy150Open alimanfoo/petl/petl/util/base.py/header