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SQL 查询在使用内部连接时返回夸大计数
原标题:SQL query returns inflated count when using inner join

我试图计算加密或拒绝加密或拒绝加密的次数, 在一个特定栏栏中出现。 下面的代码返回有问题

use DEW
SELECT Count (distinct DeviceData.machinename) As [Number Of Devices], 
DeviceData.CurrentSite, DeviceData.Country
  ,sum(case buildstatus when  encrypted  then 1 else 0 end) encrypted
  ,sum(case buildstatus when  Denied  then 1 else 0 end) Denied
FROM dbo.DeviceData
where currentsite =  REN 
group by DeviceData.Country, CurrentSite

电流是这样的:

Number of Devices SiteCode Country Encrypted Denied
       3             REN    Greece    0         3

然而,当我加上一个内在的结合

FROM dbo.DeviceData JOIN dbo.SiteList ON dbo.DeviceData.country = dbo.SiteList.Country

被拒绝更改为 33 的次数 。

知道SQL为什么要这么做吗?

最佳回答

我想希腊在 SiteList 表格中有11个网站。 因此,结果与预期的一样。

如果你采取了以下行动:

SELECT 
    DeviceData.machinename,
    SiteList.Country,
    SiteList.Site, -- Or whatever the column is called...
FROM dbo.DeviceData JOIN 
     dbo.SiteList ON 
         dbo.DeviceData.country = dbo.SiteList.Country

您将会看到有33行要返回:

MACHINENAME    COUNTRY    SITE
Machine#1      Greece     Site1
Machine#1      Greece     Site2
Machine#1      Greece     Site3
Machine#1      Greece     Site4
Machine#1      Greece     Site5
Machine#1      Greece     Site6
Machine#1      Greece     Site7
Machine#1      Greece     Site8
Machine#1      Greece     Site9
Machine#1      Greece     Site10
Machine#1      Greece     Site11
Machine#2      Greece     Site1
Machine#2      Greece     Site2
Machine#2      Greece     Site3
Machine#2      Greece     Site4
etc...

我认为你需要做的是加入 Site ,而不是 code > country

 FROM dbo.DeviceData JOIN 
      dbo.SiteList ON 
           dbo.DeviceData.CurrentSite = dbo.SiteList.Site
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