我正在尝试优化这个查询，该查询通过信誉字段（第1个）和ID字段（第2个）对帖子进行排序。没有第一个字段查询需要大约0.250秒，但有了它需要大约2.500秒（意味着慢了10倍，可怕）。有什么建议吗？

SELECT -- everything is ok here
FROM posts AS p
ORDER BY 
    -- 1st: sort by reputation if exists (1 reputation = 1 day)
    (CASE WHEN p.created_at >= unix_timestamp(now() - INTERVAL p.reputation DAY) 
        THEN +p.reputation ELSE NULL END) DESC, -- also used 0 instead of NULL
    -- 2nd: sort by id dec
    p.id DESC
WHERE p.status = 'published' -- the only thing for filter
LIMIT 0,10 -- limit provided as well

注意:
-使用InnoDB（MySQL 5.7.19)
-主要是posts表上的ID
-字段同时被索引created_at和信誉

解释结果：

# id,  select_type, table, partitions, type,  possible_keys, key,  key_len, ref,  rows,    filtered, Extra
# '1', 'SIMPLE',    'p',   NULL,       'ALL', NULL,          NULL, NULL,    NULL, '31968', '100.00', 'Using filesort'

更新^^

信誉规定：一个帖子，多少(n=信誉）天可以显示在列表的顶部。

实际上，我试图给一些帖子的声誉，可以在列表的顶部，并找到解决办法：订单的帖子由“代表”，但只有“一”天的限制。但是过了一段时间（大约2年），由于表数据量的增加，这个解决方案现在成了一个问题。如果我不能解决这个问题，那么我应该从服务中删除该功能。

更新^^

-- all date's are unix timestamp (bigint)
SELECT p.*
    , u.name user_name, u.status user_status
    , c.name city_name, t.name town_name, d.name dist_name
    , pm.meta_name, pm.meta_email, pm.meta_phone
    -- gets last comment as json
    , (SELECT concat("{", 
        '"id":"', pc.id, '",', 
        '"content":"', replace(pc.content, '"', '\\"'), '",', 
        '"date":"', pc.date, '",', 
        '"user_id":"', pcu.id, '",', 
        '"user_name":"', pcu.name, '"}"') last_comment_json 
        FROM post_comments pc 
        LEFT JOIN users pcu ON (pcu.id = pc.user_id) 
        WHERE pc.post_id = p.id
        ORDER BY pc.id DESC LIMIT 1) AS last_comment
FROM posts p
    -- no issues with these
    LEFT JOIN users u ON (u.id = p.user_id)
    LEFT JOIN citys c ON (c.id = p.city_id)
    LEFT JOIN towns t ON (t.id = p.town_id)
    LEFT JOIN dists d ON (d.id = p.dist_id)
    LEFT JOIN post_metas pm ON (pm.post_id = p.id)
WHERE p.status = 'published'
GROUP BY p.id
ORDER BY 
    -- everything okay until here
    -- any other indexed fields makes query slow, not just "case" part
    (CASE WHEN p.created_at >= unix_timestamp(now() - INTERVAL p.reputation DAY) 
        THEN +p.reputation ELSE NULL END) DESC, 
    -- only id field (primary) is effective, no other indexes 
    p.id DESC
LIMIT 0,10;

解释；

# id, select_type, table, partitions, type, possible_keys, key, key_len, ref, rows, filtered, Extra
1, PRIMARY, p, , ref, PRIMARY,user_id,status,reputation,created_at,city_id-town_id-dist_id,title-content, status, 1, const, 15283, 100.00, Using index condition; Using temporary; Using filesort
# dunno, these join's are not using, but if i remove returning fields from select part show "Using index condition"
1, PRIMARY, u, , eq_ref, PRIMARY, PRIMARY, 2, p.user_id, 1, 100.00, 
1, PRIMARY, c, , eq_ref, PRIMARY, PRIMARY, 1, p.city_id, 1, 100.00, 
1, PRIMARY, t, , eq_ref, PRIMARY, PRIMARY, 2, p.town_id, 1, 100.00, 
1, PRIMARY, d, , eq_ref, PRIMARY, PRIMARY, 2, p.dist_id, 1, 100.00, 
1, PRIMARY, pp, , eq_ref, PRIMARY, PRIMARY, 2, p.id, 1, 100.00, 
2, DEPENDENT SUBQUERY, pc, , ref, post_id,visibility,status, post_id, 2, func, 2, 67.11, Using index condition; Using where; Using filesort
2, DEPENDENT SUBQUERY, pcu, , eq_ref, PRIMARY, PRIMARY, 2, pc.user_id, 1, 100.00,