Grouped by age first category B lesson
unknown
mysql
3 years ago
391 B
5
Indexable
SELECT TIMESTAMPDIFF(YEAR, birthday, ( SELECT `start` FROM lessons WHERE student_id = students.id AND category = 'B' ORDER BY `start` ASC LIMIT 1)) AS age, count(*) AS total FROM students WHERE birthday IS NOT NULL AND deleted_at IS NULL AND EXISTS ( SELECT * FROM lessons WHERE student_id = students.id AND category = 'B') GROUP BY age
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