title: Does ClickHouse support map fields?
body: <p>I want to have a field that map from a string to a nested type:</p>
  <pre><code>CREATE TABLE table
  (
      // Other fields ...
  
      MapColumn  Map&lt;String, StructType&gt;
  )
  </code></pre>
  <p>For example, I need to do the following filter efficiently:</p>
  <pre><code>WHERE MapColumn['key'].PropertyInt32 &gt; 5
  </code></pre>
  <p>What is the best way to do this in ClickHouse?</p>