title: join on mutated column postgresql
body: <p>I have two tables with different date formats, and I want to mutate on of the columns to equalise the formats, is there any way to join on a mutated a column ?</p>
  
  <p>The query :</p>
  
  <pre><code>join table_b on table_b.date_trunc('day',day2) =  table_a.date_trunc('day',day1)
  </code></pre>
  
  <p>Is giving me </p>
  
  <pre><code>ERROR schema "table_b" does not exist
  </code></pre>