Values for a specific collection date

I am a new Cognos reports user and I do not know how to set a expression to pull values for a specific collection date. Values are entered to the database monthly (end of every mnonth). I would like to create 3 data fields (that would be dispalyed in the same row in my report) that would show me values for the most current past 3 months (for example, the most current values are for December 2012, January 2013 and February 2013. Next month the most current 3 months will be January 2013, February 2013 and March 2013). It is possible that for some of my monthly indicators will have no value entered everymonth. I still would like to see the most current 3 months with values. I hope this all makes some sense. Please help.

Hi Tom,

Which field in your database has the date when the values are entered and what format is this field in?


The field is [Value Date] and is the datatime type (2013-02-28 12:00:00.000). thank you