sql - 用where子句过滤后如何对列求和

Question

在使用 where 子句过滤查询后，我试图对查询结果求和。但是，当我尝试过时，它会将整个列的数量相加，而不考虑过滤的结果。这是我正在使用的当前代码：

FROM [MBS_STATS].[dbo].[Performance_2012Q2]



  Where dbo.Performance_2012Q2.[Current Interest Rate] >= 3.00 AND dbo.Performance_2012Q2.[Current Interest Rate] < 3.10 and dbo.Performance_2012Q2.[Monthly Reporting Period] = '03/01/2013'


Select SUM (Convert (float,(dbo.Performance_2012Q2.[Current Actual Unpaid Principal Balance]))) from dbo.Performance_2012Q2 

谁能告诉我如何对 where 子句产生的查询结果求和？谢谢！

我正在使用 SQL Server 2012

Answer 1

您似乎对 SQL 应该如何工作存在根本性的误解。您需要在单个查询中进行聚合和过滤

Select SUM (Convert (float,(dbo.Performance_2012Q2.[Current Actual Unpaid Principal   Balance]))) from dbo.Performance_2012Q2
Where dbo.Performance_2012Q2.[Current Interest Rate] >= 3.00 AND dbo.Performance_2012Q2.[Current Interest Rate] < 3.10 and dbo.Performance_2012Q2.[Monthly Reporting Period] = '03/01/2013'

Answer 2

您仍然以标准方式编写查询：

Select SUM (Convert (float,(dbo.Performance_2012Q2.[Current Actual Unpaid Principal Balance])))
from dbo.Performance_2012Q2 
Where dbo.Performance_2012Q2.[Current Interest Rate] >= 3.00
And dbo.Performance_2012Q2.[Current Interest Rate] < 3.10
And dbo.Performance_2012Q2.[Monthly Reporting Period] = '03/01/2013'

数据库引擎将首先应用您的 WHERE 子句，然后聚合结果。