MySQL kennt definierte Spalten nicht?!

[mkinzler]

SQL-Code:

select 
  *,
  (buycount / viewcount) as conversion
from (
  select 
    display_name,
    (SELECT COUNT(*) from customer_viewed_coupons_view cvcv WHERE cvcv.city_id = c.id) as view_count,
    (SELECT COUNT(*) from ordered_coupons_view ocv WHERE ocv.city_id = c.id) as buy_count,
  from cities c);