Oracle

SELECT
    EXTRACT(YEAR FROM SYSDATE) - EXTRACT(YEAR FROM BIRTHDAY) -
    CASE WHEN
        TO_CHAR(SYSDATE, 'MMDD') < TO_CHAR(BIRTHDAY, 'MMDD')
    THEN
        1
    ELSE
        0
    END
FROM
    SAMPLE

MySQL

SELECT
    (extract(YEAR from curdate()) - extract(YEAR from birth)) -
    (right(curdate(), 5) < right(birth, 5)) as age
FROM
    sample