title: How to create 'table in table' in clickhouse?
body: <p>e.g.</p>
  
  <p>In clickhouse, I want to create one table like the following structure.</p>
  
  <pre class="lang-sql prettyprint-override"><code>create table (
  time     DateTime,
  visits   array(unit) 
  )
  Engine=memory
  
  the unit struct {
   a          string, 
   btime      int64,  
   c          string, 
   e          string
  }
  </code></pre>
  
  <p>How to create the table?</p>