Select Most Recent States From History Table

Question

I have inherited a table with a structure something like this:

ID   Name   Timestamp   Data
----------------------------
1    A      40          ...
2    A               


        

Answer 1

SQL Server 2000:

SELECT
  ID, Name, Timestamp, Data
FROM
  DataTable
  INNER JOIN
  (
     SELECT ID, MAX(Timestamp) Timestamp FROM DataTable GROUP BY ID
  ) latest ON 
    DataTable.ID = Latest.ID AND 
    DataTable.Timestamp = Latest.Timestamp

Answer 2

If you are using SQL Server 2005/2008, then the CTE solution already listed by Mitch Weat is the best from a performance perspective. However, if you are using SQL Server 2000, then you can't assume there aren't duplicate Name | TimeStamp combinations. Use the following code to return only one record per name:

SELECT ID
    , Name
    , TimeStamp
    , Data
FROM DataTable dt
INNER JOIN
    (SELECT Name
    , MIN(DataTable.ID) AS MinimumID
FROM DataTable  
INNER JOIN  
    (SELECT Name
        , MAX(Timestamp) AS Timestamp 
    FROM DataTable 
    GROUP BY Name) latest 
    ON DataTable.Name = Latest.Name
    AND DataTable.Timestamp = Latest.Timestamp
GROUP BY Name) MinimumLatest
ON dt.ID = MinimumLatest.ID

So if you add another record like 9 C 30, then this will only return ID 6. If you don't go this far, then you may end up return 9 C 30 and 6 C 30.

Answer 3

Another easy way :

SELECT ID,Name,Timestamp, Data
FROM   Test_Most_Recent
WHERE Timestamp = (SELECT MAX(Timestamp)
                 FROM Test_Most_Recent
                 group by Name);

Answer 4

Assuming there are no duplicate timestamps per name, something like this should work:

SELECT ID, Name, Timestamp, Data
FROM test AS o
WHERE o.Timestamp = (SELECT MAX(Timestamp)
                     FROM test as i
                     WHERE i.name = o.name)

Answer 5

SQL Server 2005 (onwards):

WITH MostRecentRows AS
(
    SELECT ID, Name, Data,
    ROW_NUMBER() OVER (PARTITION BY Name ORDER BY TimeStamp DESC) AS 'RowNumber'
    FROM MySchema.MyTable
) 
SELECT * FROM MostRecentRows 
WHERE RowNumber = 1