title: Return all possible combinations of values within a single column in SQL
body: <p>How do I return a list of all possible combinations of values from within the same single column of database 'x'? For example I have:</p>
  
  <pre><code>    col 1,
      1
      2
      3
      4
  </code></pre>
  
  <p>And I would like to return a list of all possible combinations like,</p>
  
  <pre><code>    1,2
      1,3
      1,4
      2,3,
      2,4
      3,4
  </code></pre>
  
  <p>....</p>