使用多个JOIN优化mysql查询

Question

I am building a mysql query to access videos according to access rights, but the only one I could come up with takes up to 0.5s to execute on our server.

The access rights are rather flexible, so a bit complex. TABLES:

vod_reunion contains 1 line per video relevant columns are: Id (unique identifier) and "active"

Each video belongs to 1 or more categories as per following table:

vod_appart_droit ID_theme (Id of the categorie) ID_reunion (Id of the video, so matching the one of first table)

Each user can belong to some groups:

appartenance_groupe defines to which group belong which user: ID_groupe ID_membre Now the actual rights:

vod_droit : ID_groupe: Id of the group if the record is about managing access to a group, otherwise "-1" ID_membre: Id of the user if the record is about managing access directly to a user, otherwise "-1" ID_theme: Id of the category which the user or group may access Droit: access level for this groupe or user to the category with values: 2: access allowed 1: access allowed for videos of this category having their flag "active" set at is 1 in the first table "vod_reunion" 0: no access to this category -1: forbids access to videos of this category for this user or group, even if the same video belongs to an other category to which the same group has access.

So here is the query:

SELECT
     DISTINCT r.*, vu.vu
FROM
vod_reunion r
LEFT JOIN
    (
        vod_appart_droit ad
    INNER JOIN
        vod_droit vd
        ON
        ad.ID_theme = vd.ID_theme AND 
        (vd.Droit =2 OR vd.Droit=1)
    INNER JOIN
        appartenance_groupe ag
        ON
        vd.ID_groupe = ag.ID_groupe AND
        ag.ID_membre=11
    )
    ON
    r.Id = ad.ID_reunion AND 
    (vd.Droit =2 OR (vd.Droit=1 AND r.active=1))


    LEFT JOIN
    (
        vod_appart_droit adn
    INNER JOIN
        vod_droit vnd
        ON
        adn.ID_theme = vnd.ID_theme AND 
        vnd.Droit =-1
    INNER JOIN
        appartenance_groupe ang
        ON
        vnd.ID_groupe = ang.ID_groupe AND
        ang.ID_membre=11  
    )
    ON
    r.Id = adn.ID_reunion AND
    ag.ID_groupe = ang.ID_groupe


    LEFT JOIN
    (
        vod_appart_droit adm
    INNER JOIN
        vod_droit vdm
        ON
        adm.ID_theme = vdm.ID_theme AND 
        (vdm.Droit =2 OR vdm.Droit=1) AND
        vdm.ID_membre=11
    )
    ON
    r.Id = adm.ID_reunion AND 
    (vdm.Droit =2 OR (vdm.Droit=1 AND r.active=1))

    LEFT JOIN
    (
        vod_appart_droit adnm
    INNER JOIN
        vod_droit vndm
        ON
        adnm.ID_theme = vndm.ID_theme AND 
        vndm.Droit =-1 AND
        vndm.ID_membre=11
    )
    ON
    r.Id = adnm.ID_reunion

    LEFT JOIN 
    vod_vu vu ON r.Id=vu.ID_reunion AND vu.ID_membre='11'

WHERE
    (r.langue = 0 OR r.langue = 2) AND
    ((vd.Droit IS NOT NULL AND vnd.Droit IS NULL) OR
    (vdm.Droit IS NOT NULL AND vndm.Droit IS NULL))

Note that the where clause is actually simplified here, I only left parts related to access right, but there are then multiple criteria used for searching & sorting.

Would you have any help on how to accelerate this query ? Note that when I run it multiple times consecutively it can go extremely fast, but I guess this is due to some caching capabilities of mysql.

Thank you Timothé

Answer 1

This is too long for a comment.

First, remove the distinct if it is not necessary.

Second, write the WHERE clause as r.langue IN (0, 2) and be sure there is an index on the column.

Third, if you need the distinct, remove the joins. Instead, use NOT EXISTS in the WHERE clause.

These are some ideas that might help performance. I also assume that the obvious columns are correctly indexed (the columns used in the join s for instance).