Optimizing an inner join

Question

I need some help with the optimization of a query. I have a query that's taking too long to run 12s and I would love if I could get some help in trying to optimize it as I'm not a sql guru. Here it is :

SELECT   ID                                          ,
         user_login                                  ,
         user_nicename                               ,
         user_registered                             ,
         user_status                                 ,
         display_name                                ,
         t1.meta_value             AS account_type    ,
         1 t2.meta_value           AS views           ,
         GROUP_CONCAT(t4.term_id)  AS interests_skills,
         GROUP_CONCAT(t4.taxonomy) AS taxonomyComb    ,
         t4.term_id                                   ,
         t4.taxonomy
FROM     wp_users
         INNER JOIN wp_usermeta AS t1
         ON       (
                           t1.user_id = wp_users.ID
                  AND
                           (
                                    t1.meta_key   = 'account_type'
                           AND      t1.meta_value = 'individual'
                           )
                  )
         LEFT JOIN wp_usermeta AS t2
         ON       (
                           t2.user_id  = wp_users.ID
                  AND      t2.meta_key = 'views'
                  )
         LEFT JOIN wp_term_relationships AS t3
         ON       (
                           t3.object_id = (1000000+wp_users.ID)
                  )
         INNER JOIN wp_term_taxonomy AS t4
         ON       (
                           (
                                    t3.term_taxonomy_id = t4.`term_taxonomy_id`
                           AND      t4.taxonomy         = 'category'
                           AND      t4.term_id IN (396,410,411,416,142,417)
                           )
                  OR
                           (
                                    t3.term_taxonomy_id = t4.`term_taxonomy_id`
                           AND      t4.taxonomy         = 'skill'
                           AND      t4.term_id IN (461,463,464,466,490,468,470,491,473,474,475)
                           )
                  )
WHERE    t4.term_id IS NOT NULL
GROUP BY ID LIMIT 0,10

Here is the explain

1 SIMPLE t4 range PRIMARY,term_id_taxonomy,taxonomy term_id_taxonomy 106 NULL 17 Using where; Using temporary; Using filesort

1 SIMPLE t1 ref user_id,meta_key meta_key 768 const 3773 Using where

1 SIMPLE wp_users eq_ref PRIMARY PRIMARY 8 jasper_gi.t1.user_id 1

1 SIMPLE t2 ref user_id,meta_key meta_key 768 const 2

1 SIMPLE t3 eq_ref PRIMARY,term_taxonomy_id PRIMARY 16 func,jasper_gi.t4.term_taxonomy_id 1 Using where; Using index

Answer 1

I like the layout of your SQL - very easy to read.

Whenever I have a problem like this I try to break it down. Start with your base table without all the joins and see how it performs - look at the query plan, validate results, etc.

Then add in each join one at a time until you see the culprit. Might be a mixture of a few, might be some missing indexes, etc. But by systematically working thru the joins like this you can find the trouble-spots and get a better idea of what to do.