在SQL Server中使用For Each

Question

I have this table in my database:

StudentExam :

studentID, ExamID, EarnedMarks, Status

I want a query that returns (foreach examID check status, if 'done' return ExamID else return nothing.)

That means every student had attended the exam.

Thanks

Answer 1

To bring back all ExamId where all it's associated status are Done one way would be

SELECT ExamId 
FROM   StudentExam 
GROUP  BY ExamId 
HAVING COUNT(*) = SUM(CASE 
                        WHEN Status = 'DONE' THEN 1 
                      END) 

Or another

SELECT ExamId 
FROM   StudentExam 
WHERE  Status = 'DONE' 
EXCEPT 
SELECT ExamId 
FROM   StudentExam 
WHERE  Status <> 'DONE' 
        OR Status IS NULL