mysql逗号分隔多行
SELECT id, SUBSTRING_INDEX(SUBSTRING_INDEX(uid, ',', n), ',', - 1) AS idFROM hd_check_plain, (SELECT @rownum := @rownum + 1 AS n FROM (SELECT @rownum := 0) r, hd_check_plain) X WHERE n <= ( LENGTH(uid) - LENGTH(REPLACE(uid, ',', '')) + 1 )