MySQL Attendance System - mysql

Question

I have made an attendance system for a project, However I'm stuck right now by trying to create a query.
SELECT
COUNT(Students.idStudents) total,
SUM(case when Attendance.status LIKE 'present' then 1 else 0 end) present,
SUM(case when Attendance.status LIKE 'late' then 1 else 0 end) late,
SUM(case when Attendance.status is null then 1 else 0 end) absents
FROM Students, Schools, Tags LEFT JOIN Attendance
ON Attendance.tagCode = Tags.tagCode
WHERE Schools.idSchools = Students.idSchools
AND Tags.idStudents = Students.idStudents
This code works and generates an attendance. However this will show all the dates.
When I add in another line to specify date
AND Attendance.date = DATE(NOW());
It will not show anything..
There's 'Present', 'Late' status for the attendance however if the student's record in that table doesn't exist, it is considered as absent.
How do I do that?

Answer 1

Assuming you're using a case insensitive collation, your purported solution can be rewritten as follows:
SELECT COUNT(p.idStudents) total
, SUM(CASE WHEN a.status = 'present' THEN 1 ELSE 0 END) present -- [or just SUM(a.status = 'present')]
, SUM(CASE WHEN a.status = 'late' THEN 1 ELSE 0 END) late
, SUM(CASE WHEN a.status IS NULL THEN 1 ELSE 0 END) absents
FROM Students p
JOIN Schools s
ON s.idSchools = p.idSchools
JOIN Tags t
ON t.idStudents = p.idStudents
LEFT
JOIN Attendance a
ON a.tagCode = t.tagCode
AND a.date = CURDATE() ;
For next time: Your ERD shows 10 tables, but only 4 feature in this problem. If a table isn't likely to be part of the proposed solution, don't show it. Don't provide pictures. Instead, where possible, provide proper DDLs (and/or an sqlfiddle), TOGETHER WITH THE DESIRED RESULT SET based upon a minimal, but properly representative data set.
Welcome to SO.

Answer 2

Figured it out..
SELECT
COUNT(Students.idStudents) total,
SUM(case when Attendance.status LIKE 'present' then 1 else 0 end) present,
SUM(case when Attendance.status LIKE 'late' then 1 else 0 end) late,
SUM(case when Attendance.status is null then 1 else 0 end) absents
FROM Students, Schools, Tags LEFT JOIN (SELECT * FROM Attendance WHERE Attendance.date = NOW()) AS Attendance
ON Attendance.tagCode = Tags.tagCode
WHERE Schools.idSchools = Students.idSchools
AND Tags.idStudents = Students.idStudents

Answer 3

The problem with the original query was you were asking for students where their attendance was "NOW" where no student was ever now but they are current attending classes. They may have signed in at 8am and you run the query at 10am. You'd need to manipulate the datetime to choose your start time and end time based on the current day.
timestampadd(HOUR, 08, CURDATE()) - this will give you 8am, you'd then query for when attendance.date is greater than or equal to 8am and then potentially less than or equal to 4pm?