Question

我有两张表，比如

学生：

roll    Name
1       A
2       B
3       C

标记

roll    Mark
1       85
3       95

我想要输出

roll    Name    Grade
1       A       A
2       B       F
3       C       A+

我试过这个查询

select Stdent.Roll,Stdent.Name,Grade= case 
when (Mark between 0 and 79) then ('F')
when (Mark between 80 and 89) then ('A')
when (Mark between 90 and 100) then ('A+') end  
from Mark 
right join Stdent 
on Mark.roll=Stdent.Roll 
order by Stdent.Roll

输出在成绩列的第二行显示为null。但我希望它是F。

Answer 1

select Stdent.Roll,Stdent.Name,Grade= case 
when (func(Mark,0) between 0 and 79) then ('F')
when (Mark between 80 and 89) then ('A')
when (Mark between 90 and 100) then ('A+') end  
from Mark 
right join Stdent 
on Mark.roll=Stdent.Roll 
order by Stdent.Roll

如果使用sql server，如果是oracle nvl，则应该使用ISNULL而不是func。查看其他人的this页面。

Answer 2

您需要在案例陈述中处理Mark NULL：

SELECT  Student.Roll,
        Student.Name,
        Grade = CASE 
                    WHEN Mark.Mark BETWEEN 0 AND 79 OR Mark.Mark IS NULL THEN 'F'
                    WHEN Mark.Mark BETWEEN 80 AND 89 THEN 'A'
                    WHEN Mark.Mark BETWEEN 90 AND 100 THEN 'A+'
                END  
FROM    Mark 
        RIGHT JOIN Student 
            ON Mark.roll=Student.Roll 
ORDER BY Student.Roll

Answer 3

试试这个：

select Stdent.Roll,Stdent.Name,Grade= case 
when (IsNull(Mark, 0) between 0 and 79) then ('F')
when (Mark between 80 and 89) then ('A')
when (Mark between 90 and 100) then ('A+') end  
from Mark 
right join Stdent 
on Mark.roll=Stdent.Roll 
order by Stdent.Roll

Answer 4

select Stdent.Roll,Stdent.Name,Grade= case 
 when (NVL(Mark,0) between 0 and 79) then ('F')
 when (Mark between 80 and 89) then ('A')
 when (Mark between 90 and 100) then ('A+') end  
from Mark 
 right join Stdent 
 on Mark.roll=Stdent.Roll 
order by Stdent.Roll

使用NVL函数处理空值

在null时插入值

4 个答案: