查询以获取下表的总金额，平均值和数量

Question

如何编写SQL查询或存储过程以获取下表？

TRANCODE | SECTYPE | QUANTITY | TRADEAMOUNT
BY          CSEU     1609         19999.87 
SL          CSEU      609         7094.85

SQL查询计算：

QTY 1609-609=1000
AVG = 19999.87/1609 =12.43
TRADEAMONUT = QTY * AV = ?  

使用数量的和：

SUM 
      ( CASE 
        WHEN  TranCode ='by' THEN  CAST(Quantity as FLOAT)
        WHEN  TranCode ='ss' THEN  CAST(Quantity as FLOAT)
        WHEN  TranCode ='sl' THEN  CAST(Quantity as FLOAT) * -1
        WHEN  TranCode ='cs' THEN  CAST(Quantity as FLOAT) * -1     
  END) 

如何在SQL查询中使用数学计算？