请问，求SQL文：oracle中如何实现分支的比较大小？

Question

16:43:44 SQL> select id,name,decode(sign(grade-90),1,'优秀',
16:44:21   2  decode(sign(grade-80),1,'良好',
16:44:27   3  decode(sign(grade-60),1,'及格','不及格')
16:44:32   4  )) grade from student;ID         NAME       GRADE
---------- ---------- ------
1          csdn1      不及格
2          csdn2      及格
3          csdn3      及格
4          csdn4      良好
5          csdn5      优秀已用时间:  00: 00: 00.47
16:44:34 SQL>

Answer 1

有bug.16:47:56 SQL> select id,name,decode(sign(grade-60),-1,'不及格',
16:47:58   2  decode(sign(grade-80),-1,'及格',
16:48:07   3  decode(sign(grade-90),-1,'良好','优秀')
16:48:17   4  )) grade from student;ID         NAME       GRADE
---------- ---------- ------
1          csdn1      及格
2          csdn2      及格
3          csdn3      良好
4          csdn4      优秀
5          csdn5      优秀已用时间:  00: 00: 00.31
16:48:18 SQL>

Answer 2

select case when cast(grade as number)>=60 and cast(grade as number)<80
       then 
         '及格'
       else
         case when cast(grade as number)>=80 and cast(grade as number)<90 
         then
           '良好'
         else
           case when cast(grade as number)>=90 
           then
             '优秀'
           end
         end
       end             
from student

Answer 3

谢谢了
要的就是sign这个函数
揭帖啰

Answer 4

终于弄清楚了：
case grade
when 80 then 'normal'
when 90 then 'excellence'
end
与decode有同样的功能
但是
case 
when grade>=80 and grade<90 then 'normal'
when grade>=90 then 'excellence'
end
语句才是我想要的，两种写法，意义大相径庭