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 userl 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.username);