Question

我认为这应该很容易，但我无法弄清楚。

以下是一些背景信息：

我有两个表，称为Leases和UtilityBills。它们通过UtilityBills表中名为LeaseID的外键连接，该表引用Leases表中的主键（也称为LeaseID）。

所以这很简单 - 我正在记录每个租约的每月电表读数。

在UtilityBills表中，我有一个名为MeterReadingDate的字段，这是我在每次读取数据时存储日期的地方。

这是我的问题：

如何创建一个查询，为每次租约提供最新抄表日期和之前抄表日期？

我可以使用这个sql语句轻松地获得每个租约的最新读数：

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

我也可以使用这个sql语句获得任何给定租约的先前抄表（例如，这给了我先前的抄表租约LeaseID = 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

我无法弄清楚的是，如何将这两个语句组合起来生成一个查询，列出所有租约的第二个最近和最近的抄表日期。据我所知，我需要在这种情况下使用CROSS APPLY，但无法使其工作。谢谢！

Answer 1

如果您希望两个日期位于同一行，则可以使用ROW_NUMBER（）函数。您不需要将表连接到自身，只需使用这样的组：

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;

这里有一些其他答案建议使用RANK（）函数而不是ROW_NUMBER（）。但是，如果最后两个读数发生在同一天，RANK（）将产生意想不到的结果。

Answer 2

如果我理解正确，我认为您需要获取每个LeaseID的最新2个读数。为此;

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 3

试试这个

;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 4

对于您的特定问题，您可以通过添加group by来合并查询。这是一个例子：

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

这适用于先前的。要想更长时间，您需要一个更复杂的解决方案。。。但这不是你的问题。

Answer 5

试试这个：

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)

SQL Server：在单个查询中组合最大结果和第二大结果

5 个答案: