如何選擇由

Question

一天

我有三列

用戶ID表，計數，最大數量的用戶，日期

我希望能夠選擇爲每個最高計數的用戶ID日期。

我已經嘗試了使用內聯select語句查詢的幾個不同變體，但沒有一個100％工作，我不喜歡有三個內聯選擇的選擇。

正在做內聯選擇不使用臨時表的唯一方法嗎？什麼是解決這個問題的最好方法？

Answer 1

如果[日期]事實上是一個[日期]柱沒有時間分量：

;WITH x AS 
(
    SELECT [Date], [Count], UserID, rn = ROW_NUMBER() OVER 
    (PARTITION BY [Date] ORDER BY [Count] DESC) 
    FROM dbo.table 
) 
SELECT [Date], [Count], UserID 
FROM x 
WHERE rn = 1 
ORDER BY [Date]; 

如果[Date]是DATETIME柱上用的時間成分，則：

;WITH x AS 
(
    SELECT [Date] = DATEADD(DAY, DATEDIFF(DAY, '19000101', [Date]), '19000101'), 
    [Count], UserID, rn = ROW_NUMBER() OVER 
    (PARTITION BY DATEADD(DAY, DATEDIFF(DAY, '19000101', [Date]), '19000101') 
     ORDER BY [Count] DESC) 
    FROM dbo.table 
) 
SELECT [Date], [Count], UserID 
FROM x 
WHERE rn = 1 
ORDER BY [Date]; 

如果您想在平局的情況下選擇特定的一排，您可以在平局內爲ORDER BY添加一個平局球。如果要在綁定中包含多行，則可以嘗試將ROW_NUMBER()更改爲DENSE_RANK()。

Answer 2

爲SQL 2K5

select UserID, Count, Date 
from tb 
where Rank() over (partition by Date order by Count DESC, UserID DESC) = 1 

Answer 3

此解決方案讓你的多條記錄，如果有在計數的領帶，但是應該工作。

SELECT a.Date, a.UserId, a.[Count] 
FROM yourTable a INNER JOIN (
    SELECT MAX([Count]) as [Count], Date 
    FROM yourTable 
    GROUP BY Date 
) b ON a.[Count] = b.[Count] AND a.Date = b.Date 
ORDER BY a.Date 

Answer 4

SELECT x.* 
FROM (
    SELECT Date 
    FROM atable 
    GROUP BY Date 
) t 
CROSS APPLY (
    SELECT TOP 1 WITH TIES 
    UserID, Count, Date 
    FROM atable 
    WHERE Date = t.Date 
    ORDER BY Count DESC 
) x 

如果Date是datetime類型，並且可以具有一個非零時間組件，改變t表是這樣的：

… 
FROM (
    SELECT Date = DATEADD(DAY, DATEDIFF(DAY, 0, Date), 0) 
    FROM atable 
    GROUP BY DATEADD(DAY, DATEDIFF(DAY, 0, Date), 0) 
) t 
… 

參考文獻：

• TOP (Transact-SQL)

• Using APPLY