How to create group by age employee in php myqsl

I want to create chart.js for avarage age in my company. But I can’t create the query.

SELECT DATEDIFF(CURRENT_DATE, STR_TO_DATE(t.employee_birthday, '%Y-%m-%d'))/365 AS `ageInYears` 
FROM `employee` `t` 
WHERE `employee_birthday` BETWEEN `employee_birthday` = 20 and `employee_birthday` = 30

Answer

Presumably, employee_birthday is actually a date. At last that would make sense to me.

If you want employees between 20 and 30, then the logic is something like this:

WHERE employee_birthday >= CURDATE() - INTERVAL 30 YEAR AND
      employee_birthday < CURDATE() - INTERVAL 20 YEAR