trouble with sql

There has got to be a way to do this but I can't find the syntax.  

Essentially I need the max of column 3 grouped by column 1 and 2 and also the value of column 4 that corresponds to the returned columns 1,2, and 3.  

Here is the actual sql that I believe to be using an unnecessary join:

select ps2.periodID, ps2.projectNumber, ps2.changeDate, ps3.statusID from ( select p.periodID, ps.projectNumber, max(ps.changeDate) as changeDate
 from period p, projectStatus ps
 where ps.changeDate >= trunc( p.startDate )

       and trunc( ps.changeDate ) <= p.endDate  group by p.periodID, ps.projectNumber ) ps2, projectStatus ps3 where ps2.projectNumber = ps3.projectNumber and ps2.changeDate = ps3.changeDate  

Is there a better way to write this?  

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