根据如下表的查询结果，求以下语句的结果。
SQL＞select * from usertable；
USERID USERNAME
______
1 user1
2 null
3 user3
4 null
5 user5
6 user6
SQL＞select*from usergrade；
USERID USERNAME GRADE
______
1 user1 90
2 null 80
7 user7 80
8 user8 90
执行语句：
(1)select count(*)from usergrade where username not in(select username from usertable)；
(2)select count(*)from usergrade g where not exists(select null from usertable t where t. userid=g.userid and t.username=g.usemame)；