SELECT
CASE
WHEN TIMESTAMPDIFF(DAY, publish_time,NOW()) > 0
THEN CONCAT(TIMESTAMPDIFF(DAY, publish_time,NOW()),'天前')
WHEN TIMESTAMPDIFF(HOUR, publish_time,NOW()) > 0
THEN CONCAT(TIMESTAMPDIFF(HOUR, publish_time,NOW()),'小时前')
WHEN TIMESTAMPDIFF(MINUTE, publish_time,NOW()) > 0
THEN CONCAT(TIMESTAMPDIFF(MINUTE, publish_time,NOW()),'分前')
END AS TIME
FROM 表名