title: Can't join and select in Sequel -- PG::SyntaxError
body: <p>I'm trying to rename a column at join:</p>
  
  <pre><code>    # ...............
  
      result = DB[:my_items1].join(:my_items2, id: :my_item2_id).
            select([Sequel[:my_items2][:name].as(:my_items_name), 
                    Sequel[:my_items2][:amount].as(:my_item2_amount)
            ])
  
      # ...............
  </code></pre>
  
  <p>Exception:</p>
  
  <pre><code>Sequel::DatabaseError - PG::SyntaxError: ERROR:  syntax error at or near "AS"
  LINE 1: SELECT ("my_items2"."name" AS "my_item2_name", "...
                                           ^
  :
  </code></pre>