title: Cross Join without duplicate combinations
body: <p>I know this question is very similar to this one:
  <a href="https://stackoverflow.com/questions/12490244/symmetric-cross-join">Symmetric cross join</a>
  and this one too:
  <a href="https://stackoverflow.com/questions/7112513/combinations-not-permutations-from-cross-join-in-sql">combinations (not permutations) from cross join in sql</a></p>
  
  <p>But what about if we have two different tables, say A and B:</p>
  
  <pre><code>select A.id,B.id from A cross join B
  </code></pre>
  
  <p>and I want to consider the pair <code>(a,b)</code> equal to <code>(b,a)</code> ?</p>