SELECT tag,difficulty,ROUND((SUM(score)-max(score)-MIN(score))/(COUNT(score)-2),1) AS clip_avg_socre

FROM exam_record as er

join examination_info AS ei

WHERE er.exam_id=ei.exam_id and difficulty='hard' and tag='SQL'

select tag,difficulty,round((sum(score) - max(score)-min(score)) / (count(score)-2),1) as clip_avg_score from exam_record as er join examination_info AS ei where ei.exam_id = er.exam_id and tag = 'SQL' and difficulty = 'hard';