title: How to get rank for each row with group by in oracle sql
body: <p>I have table like below</p>
  
  <pre><code>Col_1   Col_2   Comment
  1       ABC     test
  1       ABC     test1
  1       ABC     test2
  2       DEF     xtest
  2       DEF     xtest1
  3       XYZ     ytest
  3       XYZ     ytest1
  3       XYZ     ytest2
  </code></pre>
  
  <p>And the result I want is</p>
  
  <pre><code>1       ABC     test | test1
  2       DEF     xtest | xtest1
  3       XYZ     ytest | ytest1
  </code></pre>
  
  <p>So I want to group by Col_1 and Col_2 and aggregate <strong>only the first 2 values</strong> of Comment column.</p>
  
  <p>Any idea? </p>