用于brooker的Sql存储过程计数权益营业额

我在计算布鲁克斯的成交量，总买入金额，总卖出金额。 问题是，当买方同时也是卖方时，布鲁克在买方和卖方各有一次股票交易。因此，如果布鲁克向自己出售150只股票，该交易的成交额应该是300

表:

 | InstrumentId | Price | Qty | Buyer | Seller | Date
-----------------------------------------------------
 |    265       |  22   | 100 |   A   |   B    | ----
-------------------------------------------------------
 |    265       |  23   | 150 |   A   |   A    | ----
------------------------------------------------------- 
 |    265       |  21   | 75  |   C   |   A    | ----
----------------------------------------------------

Expected result: turnover 475.
Buy total: 250.
Sell total: 225.

一种方法是：

select broker, sum(qty)
from ((select buyer as broker, qty from sales) union all
      (select seller, qty from sales)
     ) b
group by broker;