Get top 1 row of each group

Question

I have a table which I want to get the latest entry for each group. Here\'s the table:

DocumentStatusLogs Table

|ID| DocumentID | Status         


        

Answer 1

SELECT * FROM
DocumentStatusLogs JOIN (
  SELECT DocumentID, MAX(DateCreated) DateCreated
  FROM DocumentStatusLogs
  GROUP BY DocumentID
  ) max_date USING (DocumentID, DateCreated)

What database server? This code doesn't work on all of them.

Regarding the second half of your question, it seems reasonable to me to include the status as a column. You can leave DocumentStatusLogs as a log, but still store the latest info in the main table.

BTW, if you already have the DateCreated column in the Documents table you can just join DocumentStatusLogs using that (as long as DateCreated is unique in DocumentStatusLogs).

Edit: MsSQL does not support USING, so change it to:

ON DocumentStatusLogs.DocumentID = max_date.DocumentID AND DocumentStatusLogs.DateCreated = max_date.DateCreated