title: Create date column from year and doy column
body: <p>Is there a way to create a date column combining one column having the year as string and one column containing a date-of-year (doy) as integer?</p>
  <p>I am aware of methods like <code>SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');</code> or <code>SELECT to_char(date_trunc('year', now()) + interval '169 days', 'MM/DD')</code> but when trying to replace the &quot;hard coded&quot; stings with the columns I always get some kind of an error.</p>