如果该值存储为DATETIME数据类型：
SELECt YEAR(CURRENT_TIMESTAMP) - YEAR(dob) - (RIGHt(CURRENT_TIMESTAMP, 5) < RIGHt(dob, 5)) as age FROM YOUR_TABLE
考虑leap年时不太精确：
SELECt DATEDIFF(CURRENT_DATE, STR_TO_DATE(t.birthday, '%d-%m-%Y'))/365 AS ageInYears FROM YOUR_TABLE t
