SELECT

vtiger_orderitem.orderid,

	(

		SELECT

			vtiger_users.last_name

		FROM

			vtiger_users

		WHERE

			vtiger_orderitem.signatory = vtiger_users.id

	) AS signatory,

	(

		SELECT

			vtiger_users.last_name

		FROM

			vtiger_users

		WHERE

			vtiger_orderitem.servicer = vtiger_users.id

	) AS servicer

FROM

	vtiger_orderitem

SELECT

	n.orderid,

	m.last_name,

	q.last_name

FROM

	vtiger_orderitem n

LEFT JOIN vtiger_users m ON n.signatory = m.id

LEFT JOIN vtiger_users q ON n.servicer = q.id