CODEWITHSUNDEEP
mysqljoinsubquery
Moon
Moon

Reputation: 22565

Query optimazation

I have the following tables

chapters
    id
    title
videos
    id
    chapter_id
    video_url
viewed_videos
    id
    member_id
    video_id
    viewed_date

I'm using the following query now.

select 
    c.id, 
    c.title, 
    c.duration, 
    c.visible, 
    v.id as vid, 
    v.title as video_title, 
    v.chapter_id, 
    v.duration as video_duration, 
    (select count(*) from viewed_videos where video_id = v.id and member_id=32) as viewed
from chapters as c
left join videos as v
on
c.id = v.chapter_id
where
c.tutorial_id = 19

Is this the best way to query all the videos with 'viewed' field?

I think there must be a better than this way since i'm using a subquery.

Upvotes: 0

Views: 28

Answers (1)

Gordon Linoff
Gordon Linoff

Reputation: 1269773

You don't need the subquery. You can do the join and aggregation at the outer level:

select c.id, c.title, c.duration, c.visible, v.id as vid, v.title as video_title, 
       v.chapter_id, v.duration as video_duration, v.video_token, count(*) as viewed
from chapters as c left join
     videos as v
     on c.id = v.chapter_id left join
     viewed_videos vv
     on vv.video_id = v.id and member_id=32
where c.tutorial_id = 19
group by c.id, v.id;

However, the subquery is not such a bad thing. In fact, it is quite possible that the performance is better with the subquery than with this version.

Upvotes: 2

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