聚集函数

不能出现在where中

所以查出某些同学的数学分数大于平均分15分

select t1.name
from student t1, course t2, student_course t3
where t1.id = t3.student_id
  and t2.id = t3.course_id
  and t2.curse_name = 'Math'
  and t3.score > 15 + (
  									select avg(t3.score)
  									  from course t2, student_course t3
  									 where t2.id = t3.course_id
  										 and t2.curse_name = 'Math'
  )