oracle 查询类似一个学生每周每门课程数统计

查询结果有4行，为四个grade，列就是每个状态，要求就算数据库一条数据都没有，还是有4行结果（grade）显示，显示都是0

SELECT
c.CNAME,
COUNT(DISTINCT s.SNO) AS '选修人数'
FROM
score s
RIGHT JOIN course c
ON s.CNO = c.CNO
GROUP BY c.CNAME

select name,grade,status from grade

select name,grade,status from grade group by grade

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0

nvl(字段名，0)判断为空的时候替换成0

select grade,nvl(status,0) from student group by grade

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0。。。。。

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0

select grade,nvl(status,0) from tableName group by grade

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0

select grade,nvl(status,0) from student group by grade
nvl(字段名，0)判断为空的时候替换成0