Stored procedure not displaying data when null is passed into input parameter

Question

I recently started learning stored procedures in MySQL and created a procedure like this:

CREATE DEFINER=`root`@`localhost` PROCEDURE `sp_getAllDetails`(IN _student_no INT, 
IN _class_id INT, IN _subject_name VARCHAR(50) )
BEGIN
IF _student_no IS NOT NULL AND _class_id IS NULL AND _subject_name IS NULL THEN
 SELECT DISTINCT S.Student_No, S.Student_Name, C.Class_id, S.Class,
 C.Class_desc, M.Eng_marks, M.Maths_marks, M.Science_marks FROM Student S 
 INNER JOIN Marks M ON S.Student_No = M.Student_No
 INNER JOIN Class C ON M.Class_id = C.Class_id
 WHERE S.Student_No = _student_no;
 
 ELSE IF _class_id IS NOT NULL AND _student_no IS NULL AND _subject_name IS NULL THEN
 SELECT DISTINCT S.Student_Name, C.Class_id, S.Class, C.Class_desc,
 M.Eng_marks, M.Maths_marks, M.Science_marks FROM Student S 
 INNER JOIN Marks M ON S.Student_No = M.Student_No
 INNER JOIN Class C ON M.Class_id = C.Class_id
 WHERE C.Class_id = _class_id;
 
 ELSE IF _subject_name IS NOT NULL AND _class_id IS NULL AND _student_no IS NULL THEN
 SELECT DISTINCT S.Student_Name, S2.Student_No, S2.Class_id, S1.Subject_Name, 
 S1.Subject_id, S3.Eng_marks, S3.Maths_marks, S3.Science_marks
 FROM Subject1 S1 
 INNER JOIN Subject2 S2 ON S1.Subject_id = S2.Subject_id 
 INNER JOIN Subject3 S3 ON S3.Student_No = S2.Student_No
 INNER JOIN Student S ON S.Student_Name = S2.Student_Name
 WHERE S1.Subject_Name = _subject_name;
 END IF;
 END IF;
 END IF;
END

It is displaying the desired output only when I call the procedure like this in the workbench:

call school.sp_getAllDetails(401, NULL, NULL);

However, if I enter the input parameters in the dialog box from the shortcut in the left-hand menu, it is taking the same as:

call school.sp_getAllDetails(401, NULL, 'NULL');

This is not displaying any data as it is taking NULL as a string. Can I know where am I going wrong? It will be a great help. Many Thanks

Edit: Leaving the question here because anyone who's looking for the same may get some help here. Also, if anyone has a different answer can add to this.

Answer 1

Well, I figured out the problem by myself. I removed _subject_name IS NULL in both the first and the second IF condition and it worked as expected.