SQL Server：在單個查詢中結合最大結果和第二大結果

Question

我認爲這應該很容易，但我無法弄清楚。

下面是一些背景資料：

我有兩個表，稱爲租賃和UtilityBills。他們通過名爲LeaseID的外鍵連接在UtilityBills表中，該表引用了Leases表中的主鍵（也稱爲LeaseID）。

所以這非常簡單 - 我爲每個租賃記錄每月的電錶讀數。

在UtilityBills表中，我有一個名爲MeterReadingDate的字段，它用於存儲每次讀取儀表讀數的日期。

這裏是我的問題：

如何創建一個查詢，這將給我，爲每個租賃，雙方最近一次抄表日期，和之前的抄表日期？

我能夠獲得最新的抄表每個租賃很輕鬆了，使用這個SQL語句：

SELECT LeaseID, MAX(MeterReadingDate) AS MostRecentMeterReadingDate 
FROM dbo.UtilityBills 
GROUP BY LeaseID 

我也能得到之前抄表對於任何給定的租賃，使用該SQL聲明（例如，這給了我與LeaseID租賃之前抄表= 228）：

SELECT TOP 1 MeterReadingDate, LeaseID 
FROM (SELECT TOP 2 MeterReadingDate, LeaseID 
       FROM dbo.UtilityBills 
       WHERE (LeaseID = 228) 
       ORDER BY MeterReadingDate DESC) DERIVEDTBL 
ORDER BY MeterReadingDate 

我想不通，是如何將這兩個語句結合生成一個查詢，列出第二 - 最近的和最近的抄表日期，所有租約。據我所知，我需要在這種情況下使用CROSS APPLY，但無法使其工作。謝謝！

Answer 1

如果我理解正確，我認爲您需要從每個LeaseID獲取最近的2個讀數。爲此，

SELECT LeaseID, MeterReadingDate 
FROM (
    SELECT LeaseID, MeterReadingDate, 
      Rank() Over (Partition by LeaseID Order by MeterReadingDate desc) rk 
    FROM dbo.UtilityBills 
) A 
WHERE rk <3 
ORDER BY MeterReadingDate desc 

Answer 2

試試這個

;WITh CTE AS 
(
    SELECT LEASEID, MeterReadingDate, ROW_NUMBER() OVER 
         (PARTITION BY LEASEID 
         ORDER BY MeterReadingDate DESC) RN 
    FROM dbo.UtilityBills 
) 
SELECT x1.LEASEID, x1.MeterReadingDate CurrentDate, 
x2.MeterReadingDate PreviousDate 
FROM CTE x1 
LEFT OUTER JOIN CTE X2 ON x1.leaseid = x2.leaseid AND x1.rn + 1 = x2.rn 
WHERE X1.rn = 1 

Answer 3

爲您的特定問題，可以通過包括group by組合查詢。這裏是一個例子：

SELECT LeaseID, MIN(MeterReadingDate) as PriorReading, MAX(MeterReadingDate) as LatestReading 
FROM (SELECT TOP 2 MeterReadingDate, LeaseID 
     FROM dbo.UtilityBills 
     WHERE (LeaseID = 228) 
     ORDER BY MeterReadingDate DESC 
     ) DERIVEDTBL 
group by leaseid 
ORDER BY MeterReadingDate 

這適用於以前。爲了延長使用時間，您需要更復雜的解決方案。 。 。但那不是你的問題。

Answer 4

試試這個：

SELECT  
    ls.Id as 'leaseId', 
    ub.MeterReadingDate as 'MeterDate' 
FROM Leases ls 
    left outer join UtilityBills ub on ls.Id = ub.LeaseID 
    left outer join UtilityBills ub2 on ub2.LeaseID=ls.Id 
            and ub2.MeterReadingDate > ub.MeterReadingDate 
    left outer join UtilityBills ub3 on ub3.LeaseID=ls.Id 
            and ub3.MeterReadingDate > ub.MeterReadingDate 
            and ub3.MeterReadingDate < ub2.MeterReadingDate 
    left outer join UtilityBills ub4 on ub4.LeaseID=ls.Id 
            and ub3.Id is null 
            and ub4.MeterReadingDate > ub2.MeterReadingDate 
WHERE ub2.Id is null 
    or (ub3.Id is null and ub4.Id is null) 

Answer 5

如果你想在同一行中的兩個日期，你可以使用ROW_NUMBER（）函數。你不需要加入表本身，只是像這樣使用一組：

IF OBJECT_ID('dbo.UtilityBills') IS NOT NULL DROP TABLE dbo.UtilityBills; 

CREATE TABLE dbo.UtilityBills(
Id INT IDENTITY(1,1) PRIMARY KEY CLUSTERED, 
LeaseId INT, 
MeterReadingDate DATE 
); 

INSERT INTO dbo.UtilityBills(LeaseId,MeterReadingDate)VALUES 
    (1,'2012-01-01'), 
    (1,'2012-02-01'), 
    (1,'2012-03-01'), 
    (1,'2012-04-01'), 
    (2,'2012-01-02'), 
    (2,'2012-03-02'), 
    (2,'2012-05-02'), 
    (3,'2012-08-03'), 
    (3,'2012-10-03'), 
    (4,'2012-05-04'); 

SELECT LeaseId, 
MAX(CASE WHEN rn = 1 THEN MeterReadingDate END) MostRecentReadingDate, 
MAX(CASE WHEN rn = 2 THEN MeterReadingDate END) PreviousReadingDate 
FROM(
SELECT LeaseID, 
     MeterReadingDate, 
     ROW_NUMBER() OVER (PARTITION BY LeaseId ORDER BY MeterReadingDate DESC) rn 
FROM dbo.UtilityBills 
)AS U 
WHERE rn <=2 
GROUP BY LeaseId; 

這裏有一些其他的答案提示）的RANK（）函數而不是ROW_NUMBER（。但是，如果最後兩次讀數在同一天發生，RANK（）會產生意想不到的結果。