Select from a table based on the value of another table with no inter-relation

I am using sqlite3. When I run the following query it does not return any value. (It doesn't show any error either).

SELECT 
term_id, 
session_id, 
student_id , 
total,  
gpa,
grade_letter
FROM 
(
   SELECT 
     term_id, 
     session_id, 
     student_id , 
     sum(overall_term_mark +  overall_term_class_test_mark) AS total,  
     SUM(overall_term_gpa) AS gpa    

     FROM tbl_main_exam_details a
     LEFT JOIN tbl_main_exam b ON b.main_exam_id = a.main_exam_id
     WHERE session_id = 1 AND term_id = 1 AND class_id = 1
     GROUP BY student_id    
) k,
tbl_grading_system  WHERE grade_point >= k.gpa AND grade_point <= k.gpa

But If I replace the last line of the code with the following code, then it gives me my desired result.

tbl_grading_system  WHERE grade_point >= 4 AND grade_point <= 4

If I completely remove the last line of the code and don't select grade_letter from tbl_grading_system then all records show up perfectly including the gpa

So I think the query is selecting the gpa value but for some reason the last line of the code can't get the value of it and hence the query is not returning any result.

Could you please tell me where the mistake is ?

Thanks in advance.