alcite-upgrades">
  Calcite Upgrade(s)
  <a class="anchor" href="#calcite-upgrades">#</a>
</h2>
<p>In Apache Flink 1.18, Apache Calcite was gradually upgraded from 1.29 to 1.32. The immediate benefit of these upgrades
are bug fixes, a smarter optimizer and performance improvements. On a parser level, it now allows joins to be
grouped into trees using parentheses (mentioned in SQL-92) e.g. <code>SELECT * FROM a JOIN (b JOIN c ON b.x = c.x) ON a.y = c.y</code>
also see <a href="https://issues.apache.org/jira/