title: SELECT Last record in a Month based on Users table
body: <p>I have a table that is a collection entries with invoices based on users</p>
  
  <pre><code>INV_NUMBER      FK_CUST_ID  INV_DATE    FK_SALES_REP_ID 
  2000000001      25416        2/25/2013     540  
  2000000002      25409        3/3/2013      539  
  2000000003      6107         2/16/2013     539  
  2000000004      3332         2/18/2013     540  
  510370000000792 43565        12/31/2013    765  
  </code></pre>
  
  <p>How do I create a query that would give me the last <code>INV_NUMBER</code> in a month of December 2013
  of a each <code>SALES_REP</code>.</p>