我需要出一个数据统计的报表，大概要查6张表，一张表大概是200w记录左右

select dt,num,count(*) from
    (SELECT
        CONCAT(YEAR (create_time),'年',WEEK(create_time),'周') dt,
        COUNT(1) AS num
    FROM mail_record202108
    GROUP BY dt,`to` ORDER BY WEEK(create_time))t1
group by num order by dt,num;

由于数据量大而且查询复杂，一直查询超时，有什么办法吗？create_time和to都是索引