Question

I am learning to use mysql.So, I got some problems.

I have three table :users movie and movie watching history(moviewh)

the structure of movie table is:

movie_id[key]  movie_title

and users is:

user_id[key] user_name

and moviewh is:

user_id[key] movie_id[key] watching_date[key]

and my sql query is:

EXPLAIN
SELECT m.movie_id,m.movie_name_cn FROM movie AS m
LEFT JOIN moviewh AS mwh  
ON m.movie_id = mwh.movie_id
WHERE date_format(mwh.watching_date,'%Y-%m-%d') = '2010-11-01' AND mwh.user_id = 1

so . how can I optimize the table and query ??

Answer 1

Why are you doing a left join if you are only interested in seeing what movies a user has watched on a particular date?

SELECT m.movie_id,m.movie_name_cn 
FROM movie AS m, moviewh AS mwh  
WHERE m.movie_id = mwh.movie_id
      AND date_format(mwh.watching_date,'%Y-%m-%d') = '2010-11-01' 
      AND mwh.user_id = 1

assuming of course that a user can’t have watched movies that don’t exist in your db …