SQL Server 2012 - MAX（）函數

Question

我從3個單獨的員工相關表中提取數據，所有表都加入了SSN。由於有些員工多次在公司內部調動，他們在系統中有多個僱用/離職日期，因此當我從該表中抽取僱用日期時，系統會按照僱傭/離職日期的數量複製該行。這裏是因爲它拉到數據樣本：

SSN   Name  Pay_Date Hire_Date 
123456789 John Doe 5/1/2012 1/1/2001 
123456789 John Doe 5/1/2012 2/5/2005 
123456789 John Doe 5/1/2012 3/1/2012 
123456789 John Doe 5/15/2012 1/1/2001 
123456789 John Doe 5/15/2012 2/5/2005 
123456789 John Doe 5/15/2012 3/1/2012 
123456789 John Doe 5/29/2012 1/1/2001 
123456789 John Doe 5/29/2012 2/5/2005 
123456789 John Doe 5/29/2012 3/1/2012 

查詢：

SELECT 

SSN, Name, Pay_Date, Hire_Date 

FROM Personnel as PER 

LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 

LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 

ORDER BY Pay_Date(DESC) 

爲了消除與租賃日期1/1/2001和2005年2月5日的行，我嘗試使用MAX功能如下，沒有運氣。我嘗試使用以前與MAX相關的主題上發佈的各種示例，但沒有任何工作。

SELECT 

SSN, Name, Pay_Date, MAX(Hire_Date) 

FROM Personnel as PER 

LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 

LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 

GROUP BY SSN 

ORDER BY Pay_Date(DESC) 

同樣，我只需要最新僱用日期的行。所以結果應該看起來像

SSN   Name  Pay_Date Hire_Date 
123456789 John Doe 5/1/2012 3/1/2012 
123456789 John Doe 5/15/2012 3/1/2012 
123456789 John Doe 5/29/2012 3/1/2012 

Answer 1

它是最新的支付日期和僱傭日期？如果是的話，這應該工作。

SELECT 

SSN, Name, MAX(Pay_Date), MAX(Hire_Date) 

FROM Personnel as PER 

LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 

LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 

GROUP BY SSN, Name 

ORDER BY Pay_Date(DESC) 

Answer 2

要獲得最新的僱用日期行：

SELECT 
SSN, Name, Pay_Date, Hire_Date 
FROM Personnel as PER 
LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 
LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 
WHERE ROW_NUMBER() OVER (PARTITION BY SSN, ORDER BY Hire_Date DESC)=1 
ORDER BY Pay_Date DESC 

Answer 3

;WITH MyCTE AS 
(
    SELECT SSN, 
        Name, 
        Pay_Date, 
        Hire_Date, 
        ROW_NUMBER() OVER(PARTITION BY SSN, Name, Pay_Date ORDER BY Hire_Date DESC) AS rn 
    FROM  Personnel as PER 
    LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 
    LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 
) 
SELECT * 
FROM MyCTE 
WHERE rn = 1 

SQL Fiddle Demo技術Lamak在這種情況下

Answer 4

聚合函數是有問題的，因爲MAX（）進行數據不同的列可以來自您的設置中的不同行。

取而代之的是，使用窗口函數來發現每個SSN組中的哪個行具有最高（最近）的Hire_Date，然後從該子集中選擇您的結果。

SELECT SSN, Name, Pay_Date, Hire_Date 
FROM 
    (
    SELECT 

     SSN 
     , Name 
     , Pay_Date 
     , Hire_Date 
     , ROW_NUMBER() over (PARTITION BY SSN ORDER BY Hire_Date DESC) rn 
    FROM 
     Personnel as PER 

     LEFT JOIN Payroll as PAY on PER.SSN = PAY.SSN 

     LEFT JOIN HumanResources as HR on PER.SSN = HR.SSN 
    ) x 

WHERE 
    x.rn = 1 

ORDER BY Pay_Date DESC