title: Mutual Friend column, select a pair only once
body: <p>I have a table <code>likes</code>, Where ID1 likes ID2</p>
  
  <pre><code>ID1     ID2
  1025    1101
  1247    1468
  1316    1304
  1501    1934
  1641    1468
  1689    1709
  1709    1689
  1782    1709
  1911    1247
  1934    1501
  </code></pre>
  
  <p>so i am select those who like each other, that is example</p>
  
  <pre><code>1501 1934
  1934 1501
  </code></pre>
  
  <p>But i want to select each pair only once, and i am not able to do it. Can anyone point me in the right direction ? its a part of a bigger query, but this part i am not able to do.</p>
  
  <p>Thanks</p>