title: Interleave two SQL columns into paired array
body: <p>I'm trying to Interleave two SQL columns into paired array.
  How do I turn this:</p>
  
  <pre><code>id         key      val
  ---        ---      ---             
  1          a        apple
  1          b        boy
  2          x        xray
  2          y        yellow
  </code></pre>
  
  <p>into this:</p>
  
  <pre><code>new_id         array    
  ---        ---             
  1          {a,apple},{b,boy}
  2          {x,xray},{y,yellow}
  </code></pre>