title: permutation and combination
body: <p>i have a table with only one column consisiting of 5 colours-</p>
  
  <pre><code>colour
  -------
  red
  black
  white
  green 
  orange
  </code></pre>
  
  <p>I want to get all the combinations like </p>
  
  <p>(red,orange)
  (black,white) 
  .
  .
  .
  etc except the identical ones.i have tried to cross join the table with itself .</p>
  
  <pre><code>select * 
  from table1 cross join table1
  </code></pre>
  
  <p>but i did not get the desired answer.it returned all the combinations.also identical ones.how can i get it???is there any other way to do this without creating another table???</p>