_color,
               s.sl_len,
               s.sl_unit,
               s.sl_len * u.un_fact AS sl_len_cm
          FROM shoelace_data s, unit u
         WHERE s.sl_unit = u.un_name) shoelace;</PRE
><P>

     There is one difference however: the subquery's range table has two
     extra entries <TT
CLASS="LITERAL"
>shoelace old</TT
> and <TT
CLASS="LITERAL"
>shoelace new</TT
>.  These entries don't
     participate directly in the query, since they aren't referenced by
     the subquery's join tree or tar