title: Support UNION function in BigQuery SQL
body: <p>BigQuery does not seem to have support for UNION yet:
  <a href="https://developers.google.com/bigquery/docs/query-reference" rel="noreferrer">https://developers.google.com/bigquery/docs/query-reference</a></p>
  
  <p>(I don't mean unioning tables together for the source. It has that.)</p>
  
  <p>Is it coming soon?</p>