How to get passed and failed students using SQL? - sql

Question

I am trying to get those students who passed the first exams will be eligible for 2nd-month exams.
For example student_ID = 1 and Exam_ID = 1 pass then he will be eligible for the exams of Exam_ID = 2.
But the students failed in Exam_ID = 2 will not be eligible for exam_ID = 3 and passed students shouldn't be shown in Exam_ID = 2.
For exam2 entry only those students should show who passed exam1 and in exam2 will be showing for exam3 entry those who are failed in exam2. Mean the students who passed exam1 but fail in exam2.
I am confused what query will be work for this.
I tried this:
select student_Id
from Tbl_StudentsExamMarking
where Office_Id = 1
and Class_Id = 1
and Exam_Id = 1
and Status = 'Pass'
but I am getting only student_id=1 and 2 while student_id=2 passed the exam1 then he shouldn't be shown in exam1. I mean the students shouldn't show who passed the exam1 and students shouldn't show for exam2 who passed exam2.
on running query I am getting this result.
I tried to solve this problem. Kindly help me in this scenario.
Thanks.

Answer 1

You could join the table with itself and filter each join for the specific exam_id.
For example (You will need to replace #students with your table name):
In the following I make a subquery for exam_id = 1, a second subquery for exam_id = 2 and a third subquery for exam_id =3.
This gives you a "new table" that you then can filter.
SELECT
E1.studentid,
E1.Status AS [Status_exam2],
E2.Status AS Status_exam2,
E3.Status AS Status_exam3
FROM
(
-- The first exam_id as the main table as normally all students will do the first exam
SELECT *
FROM #students
Where exam_id = 1
) E1
LEFT JOIN
(
-- Left join with the second selection as maybe not all patients already did the
-- second exam
SELECT *
FROM #students
Where exam_id = 2
) E2 ON E1.studentid = E2.studentid
LEFT JOIN
(
SELECT *
FROM #students
Where exam_id = 3
) E3 ON E1.studentid = E3.studentid
With your example this gives the following output:
This "new" table, you can filter:
For example:
Patients passed exam_id1 but did not do the second or failed the second one
Add the following at the end of the above program:
WHERE E1.Status = 'Pass'
AND E2.Status is null or E2.Status = 'Fail'
This gives you the following:

Answer 2

You seem to be assuming that tests come in sequence and only depend on a single prerequisite. This isn't a recommended approach but is it the result that you need?
select Student_id, max(Exam_Id) as Last_Pass_Exam_Id
from Tbl_StudentsExamMarking
where Status = 'Passed'
group by Student_id

Answer 3

Assuming I'm understanding your challenge, try something like this:
-- Exam data mockup table and data.
DECLARE #ExamData TABLE ( Student_id INT, Class_id INT, Office_Id INT, Exam_Id INT, [Status] VARCHAR(4) );
INSERT INTO #ExamData ( Student_id, Class_id, Office_Id, Exam_Id, [Status] )
VALUES
( 1, 1, 1, 1, 'Pass' ),
( 2, 1, 1, 1, 'Pass' ),
( 9, 1, 1, 1, 'Fail' ),
( 10, 1, 1, 1, 'Fail' ),
( 1, 1, 1, 2, 'Pass' ),
( 2, 1, 1, 2, 'Fail' );
-- What exam has been passed?
DECLARE #PassedExamNo INT = 1;
-- Show students who have passed the specified exam and are eligible for the next.
-- Excludes:
-- Students who failed required exam.
-- Students who have already passed the next sequential exam.
-- Assumption: Exam ids are incremented by 1 for each sequential exam.
SELECT * FROM #ExamData AS e
WHERE
Office_Id = 1
AND Class_Id =1
AND Exam_Id = #PassedExamNo
AND [Status] = 'Pass'
AND NOT EXISTS (
SELECT * FROM #ExamData AS x WHERE
x.Office_Id = e.Office_Id AND x.Student_id = e.Student_id AND x.Exam_Id = ( e.Exam_Id + 1 ) AND x.[Status] = 'Pass'
);
Returns any student(s) who are eligible for the next exam:
+------------+----------+-----------+---------+--------+
| Student_id | Class_id | Office_Id | Exam_Id | Status |
+------------+----------+-----------+---------+--------+
| 2 | 1 | 1 | 1 | Pass |
+------------+----------+-----------+---------+--------+
You can run the above example in SSMS.

Answer 4

You can try the below query once. This will give the each student and the last exam he has taken and status
SELECT student_Id
,Exam_Id
,[Status]
FROM (
SELECT student_Id
,Exam_Id
,[Status]
,ROW_NUMBER() OVER (
PARTITION BY student_Id ORDER BY Exam_Id DESC
) [rownum]
FROM Tbl_StudentsExamMarking
WHERE Office_Id = 1
AND Class_Id = 1
) a
WHERE a.[rownum] = 1
Adding the new query as per your comment.
DECLARE #exam_id INT = 2
SELECT
student_Id
,Exam_Id
,[Status]
FROM Tbl_StudentsExamMarking
WHERE Office_Id = 1
AND Class_Id = 1
AND ((Exam_id = #exam_id AND [Status] = 'Fail')
OR (Exam_id = #exam_id - 1 AND [Status] = 'Pass'))
Sample output for Query 1

Answer 5

This is the complete answer to my query. I resolved after 5 days.
Select st.Student_Id, st.Student_Name,sm.Status,sm.Exam_Id from Tbl_StudentsExamMarking sm
inner join Tbl_Students st on st.Student_Id = sm.Student_Id
where sm.Office_Id = 1 and sm.Class_Id = 1 and sm.exam_id=2 and status='Fail' and Month(sm.Exam_Date)=08 and not exists(select * from Tbl_StudentsExamMarking as f where f.Student_Id=sm.Student_Id and f.Office_Id = sm.Office_Id and f.Status = 'pass' and f.Exam_Id = (sm.Exam_Id+1))
and exists(select * from Tbl_StudentsExamMarking as f where f.Student_Id=sm.Student_Id and f.Office_Id = sm.Office_Id and f.Status = 'Pass' and f.Exam_Id = (sm.Exam_Id-1))
and not exists(select * from Tbl_StudentsExamMarking as f where f.Student_Id=sm.Student_Id and f.Office_Id = sm.Office_Id and f.Status = 'Pass' and f.Exam_Id = (sm.Exam_Id))
--AND NOT EXISTS (SELECT * FROM Tbl_StudentsExamMarking AS x WHERE x.Office_Id = sm.Office_Id AND x.Student_id = sm.Student_id AND x.Exam_Id = ( sm.Exam_Id ) AND x.[Status] = 'Fail')
Union
Select st.Student_Id, st.Student_Name,sm.Status,sm.Exam_Id from Tbl_StudentsExamMarking sm
inner join Tbl_Students st on st.Student_Id = sm.Student_Id
where sm.Office_Id = 1 and sm.Class_Id = 1 and sm.exam_id=1 and status='Pass' and Month(sm.Exam_Date)=08
AND NOT EXISTS (SELECT * FROM Tbl_StudentsExamMarking AS x WHERE x.Office_Id = sm.Office_Id AND x.Student_id = sm.Student_id AND x.Exam_Id = ( sm.Exam_Id + 1 ) AND x.[Status] = 'Pass')
AND NOT EXISTS (SELECT * FROM Tbl_StudentsExamMarking AS x WHERE x.Office_Id = sm.Office_Id AND x.Student_id = sm.Student_id AND x.Exam_Id = ( sm.Exam_Id + 1 ) AND x.[Status] = 'Fail')