GROUP BY SQL 语句中的 Sub SELECT

Question

我有一个 table，我在其中解析了一大堆 VPN 日志。 table 没有主键字段，guid 字段是所有内容的关联方式。我想 select 行按 guid 分组。运行组内的子 select 用于特定字符串。不确定这是否有意义，这是查询：

SELECT [guid]
  ,Max([username]) AS [User]
  ,MIN([datetime]) AS Minimum
  ,Max([datetime]) AS Maximum
  ,DATEDIFF(mi, MIN([datetime]), Max([datetime])) AS "Duration in Minutes"
  ,(SELECT top 1 [data] FROM [Admin].[dbo].[VPNLogs] WHERE [data] LIKE '%The user was active for%') AS "Data"
FROM [Admin].[dbo].[temp_VPNLogs]
GROUP BY [guid]
ORDER BY "Duration in Minutes" DESC

这很好用，但数据字段的子 select 只是 returns 所有结果的同一行，当我希望它 select 这基于组时经过。每个 VPN 连接条目都有 4 行具有相同的 guid，这就是我按 guid 分组的原因，我想特别 select 每个组都有字符串 "The user was active for" 的数据字段。如果需要进一步说明，请告诉我。

谢谢！

Answer 1

co相关的子查询就是你需要的：

SELECT [guid]
  ,Max([username]) AS [User]
  ,MIN([datetime]) AS Minimum
  ,Max([datetime]) AS Maximum
  ,DATEDIFF(mi, MIN([datetime]), Max([datetime])) AS "Duration in Minutes"
  ,(SELECT top 1 [data] FROM [Admin].[dbo].[VPNLogs] V1 WHERE [data] LIKE '%The user was active for%' AND v1.guid = v.guid) AS "Data"
FROM [Admin].[dbo].[temp_VPNLogs] V
GROUP BY [guid]
ORDER BY "Duration in Minutes" DESC

GROUP BY SQL 语句中的 Sub SELECT

Sub SELECT within a GROUP BY SQL statement

sql

sql-server

greatest-n-per-group