Question

I am having some difficulties figuring out this SQL statement.

Here is the schema of the table.

studentID |subjectID | attendanceStatus | classDate | 
1234567      ...           1               .....
1234567      ...           0 

Basically I want to count the attendance percentage based on the studentID and display them in columns like this

studentID | subjectID | attendancePercentage

attendancePercentage is the number of 0s / total entries for that student

Here is what I did and it wasn’t giving the desired results.

SELECT studentID, COUNT(attendanceStatus =  0) AS Absent,
COUNT( attendanceStatus = 1) As Present
FROM attendance WHERE studentID = '1234567';

That failed.

I hope that I made sense of what I am trying to achieve.

Answer 1

I think you need use sum instead.

SELECT  studentID ,
        SUM(CASE WHEN attendanceStatus = 0 THEN 1
                 ELSE 0
            END) AS Absent ,
        SUM(CASE WHEN attendanceStatus = 1 THEN 1
                   ELSE 0
              END) AS Present
FROM    attendance
WHERE   studentID = '1234567'