题解 | #得分不小于平均分的最低分#

select min(score) as min_score_over_avg
from exam_record as er join examination_info as ei on er.exam_id = ei.exam_id 
where tag = 'SQL' and score >= (select avg(score) from exam_record as er join examination_info as ei on er.exam_id = ei.exam_id where tag = 'SQL' )

难点：子查询

为什么这里不直接score >= avg（score），而是要进行子查询，我的子查询还学的不明白，不知道使用条件。