title: Left excluding join with BigQuery
body: <p>I have two tables (A and B) having identical structures. Table B is basically a subset of Table A. I want to retrieve all the records from Table A that are not present in Table B.</p>
  <p>For this, I am considering Left Excluding Join (<a href="https://stackoverflow.com/questions/20602826/sql-server-need-join-but-where-not-equal-to/20602850">reference</a>). Here is the query I am executing:</p>
  <pre class="lang-sql prettyprint-override"><code>select a.id, a.category from a
      left join b
      on a.id = b.id
      where b.id is null;
  </code></pre>
  <p>As per BigQuery's estimate, the query will process 44.9 GiB. However, the query is taking unusually longer than expected to complete. Am I missing out on any important bit?</p>