I've been using EXPLAIN to better do my queries and spotted this:

PHP Code:
EXPLAIN SELECT films.film_titletrailers.trailer_title 
FROM films
,trailers 
WHERE trailers
.film_id=films.film_id 
ORDER BY trailers
.trailer_id DESC 
LIMIT 4 
The result I get is 48K rows must get scanned in the 'trailers' table. Why can't it just do the 4 and stop?

Thanks
Ryan