title: update query from select statement only update if the field is empty
body: <p>I am trying to write a sql statement to update a column of a table from another tables column. But I only want to update the column if its empty.  </p>
  
  <p>For example:</p>
  
  <pre><code>UPDATE
      Table
  SET
      Table.col1 = other_table.col1,
  FROM
      Table
  INNER JOIN
      other_table
  ON
      Table.id = other_table.id
  </code></pre>
  
  <p>but I want to set the Table.col1 value only if that value is empty. Whats the best way to do this? </p>