How to find total percentage of students who are absent or tardy in SQL? [closed] - mysql

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I have a grade_level and total_num_students columns but not sure how to create a column to get the percentage of students who are absent/tardy. (Each student id is unique and in both tables)
Here are the two tables:
And here is my current SQL query that I have so far:
SELECT
grade_level,
COUNT(student_attendance_log.attendance_status) AS 'total_num_students'
FROM student_info
INNER JOIN student_attendance_log
ON student_info.student_id = student_attendance_log.student_id
WHERE student_attendance_log.attendance_status = 'Tardy'
OR student_attendance_log.attendance_status = 'Absent'
GROUP BY grade_level
ORDER BY grade_level;
which produces:

Answer 1

I recommend avg() for this calculation:
SELECT grade_level, COUNT(*) as total_num_students,
AVG(CASE WHEN sal.attendance_status = 'Tardy' THEN 1.0 ELSE 0 END) as tardy_ratio,
AVG(CASE WHEN sal.attendance_status = 'Absent' THEN 1.0 ELSE 0 END) as absent_ratio
FROM student_info si INNER JOIN
student_attendance_log sal
ON si.student_id = sal.student_id
GROUP BY grade_level
ORDER BY grade_level;
Note some changes:
Table aliases makes the query easier to write and to read.
Only use single quotes for string and date constants. Don't use them for column names.
The filtering has moved from the WHERE clause to the AVG().