title: Pivot Repeated fields in BigQuery
body: <p>My Schema looks something like this:</p>
  
  <pre><code>userid:string
  timestamp:integer
  params:nested/repeated field with 2 fields
    - name:string (possible values: "a", "b","c")
    - value:string
  </code></pre>
  
  <p>I want my query to return the following:</p>
  
  <pre><code>userid, timestamp, a, b, c
  123, 1447799796, foo, bar, xyz
  233, 1447799900, bob, xxx, yyy
  :
  :
  </code></pre>
  
  <p>What's the easiest way to do this?</p>