How to sum the buy order and sell order in one row per each ticker
below should help you :  

CREATE TABLE dbo.Trading
        ([Ticker] int, [iOrder] int, [Price] int, [Amount] int)
    ;

INSERT INTO dbo.Trading
    ([Ticker], [iOrder], [Price], [Amount])
VALUES
    (1, 1, 90, 180),
    (1, 1, 89.5, 179),
    (1, -1, 91, 91),
    (2, 1, 5, 20),
    (2, -1, 4, 16),
    (2, -1, 3, 9)
;


SELECT Ticker
    ,sum(CASE 
            WHEN iorder = 1
                THEN Amount
            ELSE 0
            END) AS BuyAmount
    ,sum(CASE 
            WHEN iorder = - 1
                THEN amount
            ELSE 0
            END) AS SellAmount
FROM dbo.Trading
GROUP BY Ticker