Question

Its particular query pops up in the slow query log all the time for me. Any way to improve its efficiency?

SELECT 
    mov_id, 
    mov_title, 
    GROUP_CONCAT(DISTINCT genres.genre_name) as all_genres, 
    mov_desc, 
    mov_added, 
    mov_thumb, 
    mov_hits, 
    mov_numvotes, 
    mov_totalvote, 
    mov_imdb, 
    mov_release, 
    mov_type 
FROM movies 
LEFT JOIN _genres 
    ON movies.mov_id = _genres.gen_movieid
LEFT JOIN genres
    ON _genres.gen_catid = genres.grenre_id 
WHERE mov_status = 1 AND mov_incomplete = 0 AND mov_type = 1 
GROUP BY mov_id 
ORDER BY mov_added DESC 
LIMIT 0, 20;

My main concern is in regard to the group_concat function, which outputs a comma separated list of genres associated with the particular film, which I put through a for loop and make click-able links.

Answer 1

Do you need the genre names? If you can do with just the genre_id, you can eliminate the second join. (You can fill in the genre name later, in the UI, using a cache).

What indexes do you have?

You probably want

create index idx_movies on movies 
  (mov_added, mov_type, mov_status, mov_incomplete)

and most certainly the join index

create index ind_genres_movies on _genres
  (gen_mov_id, gen_cat_id)