Question

I have a database that looks like this:

ID   parent   name              description           _record_status   _log_user   _log_timestamp         _log_type 
--------------------------------------------------------------------------------------------------------------------
1    1        This is a rwo!    Test content          active           1           2012-01-29 15:49:21    create
2    1        This is a row!    Test Content          active           1           2012-01-29 15:52:14    revision
3    3        Another record!   More content          active           1           2012-01-29 15:58:43    create    
4    4        Deleted Record    More content          active           1           2012-01-29 15:58:43    create    
5    4        Deleted Record    More content          deleted          1           2012-01-29 15:58:43    destroy

I want to be able to select the newest row for each record, where the record isn’t deleted. So for example, the output I’d expect is:

ID   name
------------------
2    This is a row!
3    Another Record!

Is there a way to do this via SQL that is efficient, and if not, what might I want to do in PHP to accomplish this?

Would having a separate version of each table for revisions be the way to go here?

Answer 1

You’d get the highest record per parent first, then excluded anything that has been deleted:

SELECT YourTable.ID, YourTable.name
FROM YourTable INNER JOIN (
  SELECT parent, MAX(_log_timestamp) MaxLogTS
  FROM YourTable
  GROUP BY parent) T ON YourTable.parent = T.parent
                    AND YourTable._log_timestamp = T.MaxLogTS
WHERE YourTable._record_status != 'deleted'

This can be slightly optimized if you know that ID values are always in ascending time order. Then you could base the MAX record comparison on ID rather than a date and time value.