如何把这4条sql语句组合成一条?

SELECT birthday age, COUNT(*)VALUE FROM t_member WHERE TIMESTAMPDIFF(YEAR,birthday,NOW()) BETWEEN 0 AND 18

SELECT birthday age, COUNT(*)VALUE FROM t_member WHERE TIMESTAMPDIFF(YEAR,birthday,NOW()) BETWEEN 19 AND 30

SELECT birthday age, COUNT(*)VALUE FROM t_member WHERE TIMESTAMPDIFF(YEAR,birthday,NOW()) BETWEEN 31 AND 45

SELECT birthday age, COUNT(*)VALUE FROM t_member WHERE TIMESTAMPDIFF(YEAR,birthday,NOW())>45

between and 是包含边界的，从这些语句的条件来看，最终的返回其实就是 TIMESTAMPDIFF(YEAR,birthday,NOW()) 取值区间是 [0,正无穷），统一为一条SQL 条件为

WHERE TIMESTAMPDIFF(YEAR,birthday,NOW())>=0