mysql通过TEXT字段进行关联的优化方案

mysql如果通过超长的字段进行on关联，会导致效率很低，7k关联1.4k，结果为30+W的数据量，执行时间高达50秒。

将这个字段进行md5，然后再通过md5后的值进行关联，执行效率会大大优化，同样的SQL，可在5秒内完成。

select
     count(1) as cnt
from (
    select
         md5(activity.target_building_ids) as md5
    from aaaaaaaaaaaaaaaaaaaaa enroll --
) t1
left join (
    select
         md5(t21.target_building_ids) as md5
        ,t22.name
    from (select distinct bbbbbbbbbbbbbbbbbbbbb from h_activity where ifnull(target_building_ids,'') <> '') t21
    join (
        select
             bld.id
            ,proj.name
        from ccccccccccccccccccc bld --
        left join dddddddddddddddddddddd proj --
            on proj.id =bld.proj_id and proj.is_deleted=0
        where bld.is_deleted =0
    ) t22
        on instr(t21.target_building_ids,t22.id)>0
) t2 --
    on t1.md5 = t2.md5
;