Question

How to select user_ids by B meta_key and order by ratings meta_value?

    user_id    |    meta_key    |    meta_value
-----------------------------------------------------
       1                A                1
       1                B                1
       1                C                1
       1              rating             9
       8                A                1
       8                C                1
       8              rating           99999
       7                A                1
       7                B                1
       7                C                1
       7              rating            999

I need to get an IDs of users who have B meta_key and, then, to order IDs by user rating values.

Answer 1

Try this:

SELECT T1.user_id
    FROM yourtable T1 
    JOIN yourtable T2
        ON T1.user_id = T2.user_id
        AND T2.meta_key = 'rating'
    WHERE T1.meta_key = 'B'
    ORDER BY CAST(T2.meta_value AS SIGNED)