题解 | #得分不小于平均分的最低分#

select
  min(e_r.score) as min_score_over_avg
from
  exam_record e_r
  join examination_info e_i on e_r.exam_id = e_i.exam_id
where
  e_i.tag = 'SQL'
  and score >= (
    # 子查询查询出分数不为NULL也就是有效分数的平均分  
    select
      avg(e1.score)
    from
      exam_record e1
      join examination_info e2 on e1.exam_id = e2.exam_id
    where
      tag = 'SQL'
      and e1.score is not null
  )