title: How to assign row_number to new column in Oracle SQL
body: <p>My table looks like</p>
  
  <pre><code>yr     num   name
  2010    1     a
  2010    2     b
  2011    3     c
  2011    1     a
  2011    2     b   
  </code></pre>
  
  <p>I have to generate sequence for this table and it should look like below</p>
  
  <pre><code>yr     num   name   seq
  2010    1     a      1
  2011    1     a      2
  2010    2     b      1
  2011    2     b      2
  2011    3     c      1
  </code></pre>