如何根據另一列的最大值從一列中選擇一個值，如果相同，則使用另一列的最大值

Question

假設我有這張桌子：

KEY |  PID  |  ID   |  YEAR
___________________________
 1  |  123  | 999   |  2018
 2  |  123  | 999   |  2017
 3  |  123  | 999   |  2016
 4  |  456  | 888   |  2018
 5  |  456  | 999   |  2018
 6  |  456  | 777   |  2018 

我想返回唯一的KEY值和對應PID通過查詢為准行已最新YEAR該特定PID 。 如果兩個PIDs的YEAR相同，則應檢查哪個PIDs具有最新的ID 。

例如，預期結果將返回：

1  |  123  
5  |  456 

如您所見，返回1是因為它具有其余IDs之間的最新年份，而返回5是因為盡管它們都是相同的YEAR ，但ID值卻最高。

Answer 1

只需使用row_number() ：

select t.*
from (select t.*,
             row_number() over (partition by pid order by year desc id desc) as seqnum
      from t
     ) t
where seqnum = 1;

假設id是唯一的另一種方法是：

select t.*
from t
where t.id = (select maxt2.id) keep (dense_rank first order by t2.id desc)
              from t t2
              where t2.pid = t.pid 
              order by t2.year desc
             );

Answer 2

SELECT  Key, PID
FROM table
WHERE [YEAR] = (SELECT MAX([YEAR]) FROM dbo.Ptable) 
AND ID = (SELECT MAX(ID) FROM table)

Answer 3

你可以試試看

SELECT DISTINCT T.KEY,T.PID  
FROM T INNER JOIN
(
  SELECT PID,MAX(ID) MAXID
  FROM T
  GROUP BY PID
) T2 ON T2.MAXID = T.ID 
INNER JOIN
(
  SELECT PID,MAX(YEAR) AS YID
  FROM T
  GROUP BY PID
) T3 ON T3.YID = T.YEAR
ORDER BY T.KEY

sqlfiddle： http ://sqlfiddle.com/#!4/b30e1/28