Get the latest date for each record

问题

I have a History table (like a log) that records changes to parts:

TransactionID    Part ID          Description        Last Updated
1                1                Fixed O-ring       2006-03-14 20:00:04.700
2                2                Replaced coil      2009-01-02 20:00:04.700
3                1                Replaced coil      2009-01-02 20:00:04.700
4                1                Replaced LED       2002-08-20 20:00:04.700      
5                2                Sealed leakage     2007-03-08 20:00:04.700   
6                3                Replace connector  2004-05-16 20:00:04.700

I have another table that will show what each Part ID stands for, but that is not the problem I'm facing now. I'm required to write a query that returns the latest maintenance done on every parts. So in this case, my expected output would be:

TransactionID    Part ID          Description        Last Updated
2                2                Replaced coil      2009-01-02 20:00:04.700    
3                1                Replaced coil      2009-01-02 20:00:04.700 
6                3                Replace connector  2004-05-16 20:00:04.700

Explanation: For example, the latest maintenance for Part ID #1 was completed on 2009-01-02 20:00:04.700 and so on.

I have tried SELECT DISTINCT but it won't work because basically every rows will be different. I'm completely out of clue. And if I use MAX(Last Updated), it will only return one row of the entire table.

Edited: In any case, I am NOT allowed to use Dynamic query.

回答1:

SELECT TransactionID
      ,PartID
      ,[Description]
      ,[Last Updated]
FROM (
    SELECT TransactionID
          ,PartID
          ,[Description]
          ,[Last Updated]
          ,ROW_NUMBER() OVER (PARTITION BY [PartID] ORDER BY [Last Updated] DESC) RN 
    FROM TableName
    )A
WHERE A.RN = 1

Or you can use CTE

;WITH CTE AS
  (
    SELECT TransactionID
          ,PartID
          ,[Description]
          ,[Last Updated]
          ,ROW_NUMBER() OVER (PARTITION BY [PartID] ORDER BY [Last Updated] DESC) RN 
    FROM TableName
  )
SELECT TransactionID
      ,PartID
      ,[Description]
      ,[Last Updated]  
FROM CTE 
WHERE A.RN = 1

回答2:

select 
    TransactionID, PartID, Description, LastUpdated
from 
    History H
where
    LastUpdated = 
    (
        select 
            max(LastUpdated) 
        from 
            History
        where
            PartID = H.PartID
    )

回答3:

Here's How I would do it

 ;WITH CTE AS 
 (
 Select PartId, MAX(LASTUPDATED) as 'MAXX' from part group by PartId
 ) 
 Select TransActionId, p.PartId, Description, p.LASTUPDATED
 from Part p
 inner join CTE on p.LastUpdated = CTE.MAXX
                and p.PartId = CTE.PartId

回答4:

SELECT t.TransactionID, t.PartID, t.Description, t.LastUpdated
FROM History t
JOIN (SELECT PartID, MAX(TransactionID)
FROM History
GROUP BY PartID) t2 ON t.PartID = t2.PartID
AND t.TransactionID = t2.TransactionID

will also work.

来源：https://stackoverflow.com/questions/25855021/get-the-latest-date-for-each-record

标签

sql

sql-server

stored-procedures

greatest-n-per-group