how to generate student attendance percentage per course, when they have specific day in a week - mysql

Question

hi guys i really newbie in sql, i need help to generate percentage of attendance, here is the table:
Table Schedule
Schedule_ID Course_ID Lecture_ID Start_Date End_Date Course_Days
1 1 11 2019-09-09 2019-12-08 2,4,6
2 3 4 2019-09-09 2019-12-08 3,4
3 4 13 2019-09-09 2019-12-08 2,5
4 5 28 2019-09-09 2019-12-08 3
5 2 56 2020-01-27 2020-04-26 2,4
6 7 1 2020-01-27 2020-04-26 4,5
7 1 11 2020-01-27 2020-04-26 2,4,6
8 7 22 2020-01-27 2020-04-26 2,3
9 8 56 2020-01-27 2020-04-26 5
10 3 37 2020-01-27 2020-04-26 5,6
Reference of days of week used in this data.
1: Sunday, 2:Monday, 3:Tuesday, 4:Wednesday, 5:Thursday, 6:Friday, 7:Saturday
Table course_attendance
ID STUDENT_ID SCHEDULE_ID ATTEND_DT
1 1 2 2019-09-10
2 1 2 2019-09-11
3 1 2 2019-09-17
4 1 2 2019-09-18
......
46 2 1 2019-12-02
47 2 1 2019-09-11
48 2 1 2019-09-18
49 2 1 2019-09-25
50 2 1 2019-10-09
51 2 1 2019-10-16
....
111 6 1 2019-09-23
112 6 1 2019-09-30
113 6 1 2019-10-07
114 6 1 2019-10-14
table student
ID NAME
1 Jonny
2 Cecilia
3 Frank
4 Jones
5 Don
6 Harry
i need to show up like this :
STUDENT_ID NAME Course_ID Attendance rate
1 Jonny 1 82%
2 Cecilia 1 30%
3 Frank 3 100%
4 Jones 2 100%
5 Don 2 25%
6 Harry 4 40%
EDIT this my last step to get percentage:
result:
with main as (
select ca.STUDENT_ID,
ca.SCHEDULE_ID,
s.COURSE_ID,
co.NAME as course_name,
st.NAME,
count(ca.ID) as total_attendance,
((CHAR_LENGTH(s.COURSE_DAYS) - CHAR_LENGTH(REPLACE(s.COURSE_DAYS , ',', '')) + 1) * 13) as attendance_needed
from univ.course_attendance ca
left join univ.schedule s on ca.SCHEDULE_ID = s.ID
left join univ.student st on ca.SCHEDULE_ID = st.ID
left join univ.course co on ca.SCHEDULE_ID = co.ID
group by ca.STUDENT_ID, ca.SCHEDULE_ID
)
select *,total_attendance/attendance_needed as attendance_percentage
from main
order by 1,2;

Answer 1

This can be done following three steps.
Step 1: Calculate the total number of days a particular course of a schedule has. It's a good thing the start_date is always on Monday and the end_date is always on Sunday, which makes the week complete and saves some trouble. By calculating the total number of weeks a course go through and the number of days a week has for that course, we can get the total number of days a particular course of a schedule has.
Step 2:Calculate the total number of days a student for a schedule. This is done fairly easily. Note: As the majority part of the table has been skipped and the OP has yet to provide the complete data set, I could only have 14 existing rows provided.
Step 3: Calculate the percentage for the attendance using the result from the above two steps and get other required columns.
Here is the complete statement I wrote and tested in workbench:
select t2.student_id as student_id,`name`,course_id, (t2.total_attendance/t1.total_course_days)*100 as attendance_rate
from (select schedule_id,course_id,
length(replace(course_days,',',''))*(week(end_date)-week(start_date)) as total_course_days
from Schedule) t1
JOIN
(select count(attend_dt) as total_attendance,student_id,schedule_id
from course_attendance group by student_id, schedule_id) t2
ON t1.schedule_id=t2.schedule_id
JOIN
student s
ON t2.student_id=s.id;
Here is the result set ( the attendance_rate is not nice due to the abridged course_attendance table):
student_id, name, course_id, attendance_rate
2, Cecilia, 1, 15.3846
6, Harry, 1, 10.2564
1, Jonny, 3, 15.3846