SELECT orderdtl.partnum, orderdtl.docunitprice, orderhed.orderdate
FROM mfgsys80.dbo.orderdtl AS orderdtl, mfgsys80.dbo.orderhed AS orderhed
INNER JOIN(
    SELECT orderdtl.partnum, MAX(orderhed.orderdate) AS 'maxDate'
    FROM mfgsys80.dbo.orderdtl AS orderdtl, mfgsys80.dbo.orderhed AS orderhed
    GROUP BY orderdtl.partnum
) AS Temp
    ON orderdtl.partnum = Temp.partnum AND orderhed.orderdate = Temp.maxDate
WHERE orderdtl.ordernum = orderhed.ordernum AND ((orderdtl.custnum=74))
ORDER BY orderdtl.partnum