如何按值排序SQL行？

Question

如何选择 user_ids 按B meta_key和按评分排序 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

我需要获取具有 B meta_key的用户的ID，然后按用户评级值订购ID。

Answer 1

试试这个：

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)

Answer 2

为此，您需要自我加入：

select t.*
from t left outer join
     (select t.user_id, max(meta_value) as rating
      from t
      where t.meta_key = 'rating'
      group by t.user_id
     ) r
     on t.user_id = r.user_id
where meta_key = 'B'
order by r.rating