title: Concatenating distinct column values to a string
body: <p>I want to select distinct combinations of columns to a string. I do not know how to do it in a query. The scenario is as under</p>
  
  <pre><code>c1   c2   c3
  a     1    x
  b     2    x
  b     2    y
  </code></pre>
  
  <p>I want a resultset like</p>
  
  <pre><code>a:1:x
  a:1:y
  a:2:x
  a:2:y
  b:1:x
  b:1:y
  b:2:x
  b:2:y
  </code></pre>
  
  <p>Any suggestions on how to do it?</p>