SQL Server 2012-MAX（）函数

Question

I am pulling data from 3 separate employee related tables, all joined on SSN. Because some employees have transferred within the company multiple times they have multiple hire/separation dates in the system, so when I pull from that table with the hire dates, it duplicates the row by the number of hire/separation dates in the system. Here's the data sample as it's pulled:

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

The query:

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)

To eliminate the rows with hire dates 1/1/2001 and 2/5/2005, I tried using the MAX function as follows with no luck. I tried using a variety of the examples posted on previous topics related to MAX but nothing is working.

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)

Again, I just need the row with the latest hire date. So the outcome should look like

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

;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 Powered by Lamak

Answer 2

Is it the latest Pay date and hire date? if so this should work.

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 3

To get the row with the latest hire date:

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 4

Aggregate functions in this case are problematic because MAX() data for different columns can come from different rows in your set.

Instead, use window functions to discover what row in each group of SSNs has the highest (most recent) Hire_Date and then select your results from that subset.

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