Question

我正在使用SQL Server 2005.我在查询中使用Count() 3次

select    
    p.side,
    p.uid as uid,
    count (p.side) as cside,
    (count (p.side)/ 3) as pairs,
    ((count (p.side)/ 3) * 15 ) as commisonPrice
from  
    tempComm as p
group by 
    p.side , p.uid
order by 
    p.uid;

它给了我正确的输出，但问题是如何在我的查询中使用这种双重性来阻止？

Answer 1

select 
    side,
    uid,
    cside,
    cside/3 as pairs,
    cside/3*15 as commisonPrice 
from
(
    select
    p.side ,
    p.uid as uid , 
    count (p.side) as cside
    from tempComm as p 
    group by p.side , p.uid
) t
order by uid;

Answer 2

这样做的方法很多。

<强> 1。 Common Table Expression - 在SQL Server 2005中引入

;用cte as（

    select    
          p.side,
          p.uid as uid,
          count (p.side) as cside
    from  tempComm as p
    group by p.side , p.uid

)

select * , cside / 3 as pairs , (cside / 3) * 15 as commisonPrice
from cte
order by p.uid;

<强> 2。派生表

select 
    side,
    uid,
    cside,
    cside/3 as pairs,
    (cside/3)*15 as commisonPrice 
from
(
    select
    p.side ,
    p.uid as uid , 
    count (p.side) as cside
    from tempComm as p 
    group by p.side , p.uid
) t
order by uid;

其他方法是使用临时表，您必须首先插入数据并在列上执行进一步操作的视图，但我不认为它们是您的问题所必需的。

注意：

如果需要，CTE和派生表只能使用一次对您的数据执行多个操作，然后使用临时表
性能方面，CTE和派生表具有相似的性能，它只是一个偏好问题，你想要哪个更具可读性

SQL server Query Count（）优化

2 个答案: