title: Select most frequent
body: <p>I wounder if its possible to find out using sql the most frequent pairs of numbers which appear in the table. ie: 
  I've got few columns populated with numbers: </p>
  
  <pre><code>num1, num2, num3, num4, num5, num6
  2      3      4     5     6    7
  </code></pre>
  
  <p>Of course the number of rows is larger but you got an idea.. 
  The goal is to display for example 10 pairs of numbers which appeared in rows. </p>
  
  <p>Please let me know if its possible, or I should rather perform a "brute-force" kind of solution. </p>
  
  <p>Regards</p>