select round(avg(score),3) as avg_score from
(select distinct u.user_id,u.score
from recommend_tb r
join user_action_tb u
on r.rec_user = u.user_id
where r.rec_info_l = u.hobby_l)a

先将两张表相连，再添加条件推荐内容一致，再在外层计算平均分，记得要加distinct，因为不加的话会把向103推荐的不正确内容也算进去，又计算一遍