Question

I have several versions assigned to a DocumentID.

DocID  Version
ABC    1
ABC    2
ABC    3
DEF    1
DEF    2

How can I delete the older versions and only keep the most recent? After the delete, this should remain in the table:

DocID  Version
ABC    3
DEF    2

Answer 1

SQL Server 2005+:

;WITH x AS (SELECT DocID, Version, rn = ROW_NUMBER() OVER 
  (PARTITION BY DocID ORDER BY Version DESC)
  FROM dbo.tablename
)
DELETE x WHERE rn > 1;

For SQL Server 2000 it’s a little more complex. (It’s always useful to include version information.)

DELETE t
FROM dbo.tablename AS t
LEFT OUTER JOIN 
(
  SELECT DocID, Version = MAX(Version)
  FROM dbo.tablename
  GROUP BY DocID
) AS t2
ON t.DocID = t2.DocID
AND t.Version = t2.Version
WHERE t2.DocID IS NULL;

Apparently this latter query will work in MySQL as well (thanks @bluefeet).

For MySQL you’re on your own, you may be better off posting a completely different question.