List the names of all users.
select name from useracct
Only show those who gave reviews.
select distinct t1.name from useracct as t1 join review as t2 on t1.u_id = t2.u_id
Include the ratings given by each of them.
select t1.name, t2.rating from useracct as t1 join review as t2 on t1.u_id = t2.u_id
Only show their name and the average rating given by each of them.
select t1.name, avg(t2.rating) from useracct as t1 join review as t2 on t1.u_id = t2.u_id group by t2.u_id