title: Need to view time series monthly in Superset Time Series - Line Chart
body: <p>I need to view time series monthly. I'm able to get the chart with Time Grain set as "Time Column" but when I select "month" I get the following error. </p>
  
  <blockquote>
    <p>(psycopg2.ProgrammingError) function date_trunc(unknown, unknown) is not unique LINE 1: SELECT DATE_TRUNC('month', 'datetime') AS __timestamp, ^ HINT: Could not choose a best candidate function. You might need to add explicit type casts.</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/xTA2L.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xTA2L.png" alt="enter image description here"></a></p>
  
  <p>Would be much appreciated if you can help solving above issue.</p>