title: select distinct two columns width other columns
body: <p>quick example<br></p>
  
  <pre><code>sender_id  ||  receiver_id 
   25        ||     30 
   25        ||     32 
   30        ||     25 
   30        ||     20 
   20        ||     25 
  </code></pre>
  
  <p>I want output like this:</p>
  
  <pre><code>sender_id  ||  receiver_id
     25      ||     30
     25      ||     32
     30      ||     20
     20      ||     50
  </code></pre>
  
  <p>what query should be <br>
  any one can help <br>
  note: i want to select another columns in the selection </p>