SELECT YEAR (curdate()) -
IF (length(CERTIFICATE_NO) = 18,substring(CERTIFICATE_NO, 7, 4),
IF (length(CERTIFICATE_NO) = 15,concat('19',substring(CERTIFICATE_NO, 7, 2)),NULL)) AS age FROM system_user
SELECT YEAR (curdate()) -
IF (length(CERTIFICATE_NO) = 18,substring(CERTIFICATE_NO, 7, 4),
IF (length(CERTIFICATE_NO) = 15,concat('19',substring(CERTIFICATE_NO, 7, 2)),NULL)) AS age FROM system_user