select tag,difficulty,

round( (sum(score)-max(score) - min(score))/(count(score) - 2) ,1)

from

(select e_i.exam_id,e_i.tag,e_i.difficulty,e_r.score

from examination_info e_i

join exam_record e_r

on e_i.exam_id = e_r.exam_id

where tag = 'SQL'

and difficulty = 'hard')tmp

group by 1,2