title: BigQuery: convert epoch to TIMESTAMP
body: <p>I'm trying to range-join two tables, like so</p>
  
  <pre><code>SELECT *
  FROM main_table h
  INNER JOIN
      test.delay_pairs d
  ON
      d.interval_start_time_utc &lt; h.visitStartTime
      AND h.visitStartTime &lt; d.interval_end_time_utc
  </code></pre>
  
  <p>where <code>h.visitStartTime</code> is an <code>INT64</code> epoch and <code>d.interval_start_time_utc</code> and <code>d.interval_end_time_utc</code> are proper <code>TIMESTAMP</code>s.</p>
  
  <p>The above fails with</p>
  
  <pre><code>No matching signature for operator &lt; for argument types: TIMESTAMP, INT64. Supported signature: ANY &lt; ANY
  </code></pre>
  
  <p>Neither wrapping <code>h.visitStartTime</code> in <code>TIMESTAMP()</code> nor <code>CAST(d.interval_start_time_utc AS INT64)</code> work. How do I make the two comparable in BigQuery's Standard SQL dialect?</p>