Mysql example of converting birth date into age and grouping and counting the number of people

SELECT * FROM `student`

SELECT id, name, birthday, TIMESTAMPDIFF(YEAR,student.birthday,CURDATE()) as age FROM `student`

SELECT
	GROUP_CONCAT(a.id) as ids,
	GROUP_CONCAT(a.name) as names,
	CASE
		WHEN a.age<18 THEN 'teen'
		WHEN a.age>=18 AND a.age< 40 THEN 'youth'
		WHEN a.age>=40 AND a.age< 60 THEN 'middle-aged'
	END as age,
	count(a.id) as count
FROM
	(SELECT id, name, birthday, TIMESTAMPDIFF(YEAR,student.birthday,CURDATE()) as age FROM `student`) as a
GROUP BY
	CASE
		WHEN a.age<18 THEN 'teen'
		WHEN a.age>=18 AND a.age< 40 THEN 'youth'
		WHEN a.age>=40 AND a.age< 60 THEN 'middle-aged'
	END