title: Extract hour from timestamp in string format on bigQuery
body: <p>I have a timestamp that is in the string format that looks like <code>2010-02-02T07:54:40Z</code>. How can I get the <code>HOUR</code> from this timestamp?</p>
  <p>I tried <code>SELECT dt, EXTRACT(HOUR FROM dt) FROM table</code> but I am getting this error:</p>
  <pre><code>No matching signature for function EXTRACT for argument types: DATE_TIME_PART FROM STRING. Supported signatures: EXTRACT(DATE_TIME_PART FROM DATE); EXTRACT(DATE_TIME_PART FROM TIMESTAMP [AT TIME ZONE STRING]); EXTRACT(DATE_TIME_PART FROM DATETIME); EXTRACT(DATE_TIME_PART FROM TIME); EXTRACT(DATE_TIME_PART FROM INTERVAL) 
  </code></pre>
  <p>How do I get the <code>HOUR</code> from <code>2010-02-02T07:54:40Z</code>?</p>