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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_subdomain_ops_at_txid(self, txid, cur=None):
 """ Given a txid, get all subdomain operations at that txid. Include unaccepted operations. Order by zone file index """

        get_cmd = 'SELECT * FROM {} WHERE txid = ? ORDER BY zonefile_offset'.format(self.subdomain_table)

        cursor = None
        if cur is None:
            cursor = self.conn.cursor()
        else:
            cursor = cur

        db_query_execute(cursor, get_cmd, (txid,))

        try:
            return [x for x in cursor.fetchall()]
        except Exception as e:
            if BLOCKSTACK_DEBUG:
                log.exception(e)

            return []