The grading of the students based on the marks they have obtained is done as follows:

40-50  - Second class
50-60  - First Class
60-80  - First Class
80-100 - Distinctions.

The table Stud for the above query is given as:

ID|Name     |Marks                                                                                                                                                                           
11|Britney  | 95    
12|Dyana    | 55    
13|Jenny    | 66    
14|Christene| 88    
15|Meera    | 24    
16|Priya    | 76    
17|Priyanka | 77    
18|Paige    | 74    
19|Samantha | 87    
21|Julia    | 96    
27|Evil     | 79    
29|Jane     | 64    
31|Scarlet  | 80    
32|Kristeen |100    
34|Fanny    | 75    
37|Belvet   | 78
38|Danny    | 75

I’ve tried creating the grade table with assigning the grades first to the table with the following query:

Select from stud Grade=Case 
when marks>100 then 'Distinction' 
when 80>70 and marks<100 then 'Distinction' 
when marks>60 and marks<80 then 'First Class' 
when marks>50 and marks<60 then 'First Class' 
when marks>40 and marks<50 then 'Second Class' 
when marks<40 then 'Fail' 
else 'No Grade Available' end Grade ;