Can't write select statement in avg aggregate function?

bellers

Like the title, does it have to be listed?

zeonic

select avg(t.id) from (select top 10 id from sysobjects order by id)t

bellers

What if I use avg in the update statement?

Change the grade of student No. 105 for elective course No. 203 to the average grade of the changed course.
update elective set score=avg(select score from elective where course number=203) where student number=105

How to change this to be correct?
It shouldn't be necessary to post the structure and data of the entire database.

mydriver

UPDATE elective
SET score=(SELECT AVG(score) FROM elective WHERE course number=203)
WHERE student ID=105