如何分組和計數組中的項目並獲得整行？

Question

該查詢獲取所需的行 - 按主題組織 - 我也想知道每個組中的項數。

SELECT log.* FROM [hm_deliverylog] AS log 
WHERE log.deliveryid IN 
    (
     SELECT MAX([deliveryid]) FROM [hm_deliverylog] 
     WHERE [deliverytime] > DATEADD(HOUR, -12, GETDATE()) 
     GROUP BY deliverysubject 
    ) 

ORDER BY deliveryid DESC 

如何計算組？像下面一樣？

SELECT joined.groupcount, log.* FROM [hm_deliverylog] AS log 

P.S：想象一下Gmail收件箱;它顯示最新的消息並顯示消息計數。我想組相同主題的消息，並盡數...

Answer 1

一種方法是把COUNT()計算的子查詢，而不是使用IN，使之成爲派生表要加入：

SELECT log.* 
    , grp.cnt AS groupcount 
FROM 
    [hm_deliverylog] AS log 
    JOIN 
    (
     SELECT MAX([deliveryid]) AS deliveryid 
      , COUNT(*) AS cnt 
     FROM [hm_deliverylog] 
     WHERE [deliverytime] > DATEADD(HOUR, -12, GETDATE()) 
     GROUP BY deliverysubject 
    ) AS grp 
    ON grp.deliveryid = log.deliveryid 
ORDER BY 
    log.deliveryid DESC ; 

Answer 2

您可以使用OVER clause：

SELECT COUNT(deliveryid) OVER (PARTITION BY deliverysubject) As GroupCount 

確定行集的劃分和排序的 相關的窗口功能被應用之前。也就是說，OVER子句 在查詢結果 集內定義了一個窗口或用戶指定的一組行。窗口函數然後計算 窗口中每行的值。您可以使用帶有函數的OVER子句來計算彙總值，例如移動平均值，累計彙總數，運行總計數 或每組最高結果N。

Answer 3

SELECT log.*, COUNT(*) OVER (PARTITION BY deliverysubject) AS groupcount 
FROM [hm_deliverylog] AS log 
GROUP BY deliverysubject