例如
SELECT userid, `migrate_time` FROM member WHERE STATUS =0 AND id =3 ORDER BY ( update_time IS NULL ), update_time ASC LIMIT 0 , 30
SELECT * FROM your_table ORDER BY (date_column IS NULL), date_column ASC
參考：http://stackoverflow.com/questions/8510632/php-mysql-order-by-date-but-empty-dates-last-not-first