title: SQL get unique combinations of a field
body: <p>I have a table called T1 as below:</p>
  
  <pre><code>id value
  1 C
  2 B
  3 A
  </code></pre>
  
  <p>How can I find all the pairs of value, one pair for each unique combination(order does not matter), ordered by the values in the pair? Expected output below:</p>
  
  <pre><code>A B
  A C
  B C
  </code></pre>