title: populating missing rows in oracle sql
body: <p>I have following data:</p>
  
  <pre><code>date          product    amount
  2013-01-31    a1           100
  2013-02-28    a1           200
  2013-01-31    b1           700
  2013-04-30    b1           100
  2013-06-30    b1          1300
  2013-03-31    c1            10
  2013-07-31    c1            70
  </code></pre>
  
  <p>Is it possible to create query in sql/plsql that would populate missing rows based on dates? I mean i would like to get following result:</p>
  
  <pre><code>date          product    amount
   2013-01-31    a1           100
   2013-02-28    a1           200
   2013-01-31    b1           700
  *2013-02-28    b1           500*
  *2013-03-31    b1           300*
   2013-04-30    b1           100
  *2013-05-31    b1           700*
   2013-06-30    b1          1300
   2013-03-31    c1            10
  *2013-04-30    c1            25*
  *2013-05-31    c1            40*
  *2013-06-30    c1            55*
   2013-07-31    c1            70
  </code></pre>
  
  <p>i.e. create missing dates, duplicate product code and calculate amount.</p>