SQL Server 2012 - MAX（）函数

Question

我从3个单独的员工相关表中提取数据，所有表都加入了SSN。由于有些员工多次在公司内部调动，他们在系统中有多个雇用/离职日期，因此当我从该表中抽取雇用日期时，系统会按照雇佣/离职日期的数量复制该行。这里是因为它拉到数据样本：

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 

查询：

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) 

为了消除与租赁日期1/1/2001和2005年2月5日的行，我尝试使用MAX功能如下，没有运气。我尝试使用以前与MAX相关的主题上发布的各种示例，但没有任何工作。

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) 

同样，我只需要最新雇用日期的行。所以结果应该看起来像

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雇佣日期？如果是的话，这应该工作。

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

要获得最新的雇用日期行：

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技术Lamak在这种情况下

Answer 4

聚合函数是有问题的，因为MAX（）进行数据不同的列可以来自您的设置中的不同行。

取而代之的是，使用窗口函数来发现每个SSN组中的哪个行具有最高（最近）的Hire_Date，然后从该子集中选择您的结果。

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