title: How to group by time intervals with Google BigQuery
body: <p>I have TIMESTAMP weather data recorded every 5 minutes that I want to group in 15 minute intervals. I found the floor function below that looked promising, but BQ does not support the UNIX_TIMESTAMP function</p>
  
  <pre><code>SELECT
      FLOOR(UNIX_TIMESTAMP(utc_timestamp)/(15 * 60)) AS timekey
  GROUP BY
      timekey
  </code></pre>
  
  <p>What is the best way to do this?</p>