;WITH MyData (orderid, Invoice, netprice, pricechange) AS (
        SELECT 1234,98989,39.99,' '
        UNION ALL SELECT 2222, 98989, 39.99,' '
        UNION ALL SELECT 3333, 98989, 45.00, 'x'
        UNION ALL SELECT 4444, 98989, 39.99,' '
        UNION ALL SELECT 5343, 98989, 39.99,' '
        UNION ALL SELECT 4321, 98989, 37.00, 'x'
        UNION ALL SELECT 2313, 98989, 42.00, 'x'
        UNION ALL SELECT 4545, 98989, 39.99,' '
        UNION ALL SELECT 3211, 98989, 39.99,' '
        UNION ALL SELECT 1122, 77277, 45.00,' ' 
        UNION ALL SELECT 2332, 77277, 45.00,' '
        UNION ALL SELECT 4455, 77277, 30.00, 'x'
        UNION ALL SELECT 6989, 77277, 45.00,' '
        UNION ALL SELECT 3493, 77277, 55.00, 'x'
        UNION ALL SELECT 3434, 77277, 45.00,' '
        ),
    FirstOrder AS (
        SELECT orderid, invoice, netprice
        FROM (
            SELECT orderid, invoice, netprice
                ,n=ROW_NUMBER() OVER (PARTITION BY invoice ORDER BY orderid)
            FROM MyData) a
        WHERE n=1
        )
SELECT a.orderid, a.invoice, a.netprice, a.pricechange
    ,mypricechange=CASE WHEN a.netprice <> b.netprice THEN 'x' ELSE ' ' END
FROM MyData a
JOIN FirstOrder b ON a.invoice = b.invoice 
ORDER BY a.Invoice, a.orderid