mysql查询去重

mysql两个字段关联查询去重

//查询重复
SELECT * from (SELECT *, CONCAT(a,b) as aAndb from tablename) t WHERE t.aAndb in
(
SELECT aAndb from (SELECT CONCAT(a,b) as aAndb from tablename) tt GROUP BY aAndb HAVING count(aAndb ) > 1
);

//去重
DELETE from tablename WHERE id not in
( SELECT maxid from (SELECT MAX(id) as maxid, CONCAT(a,b) as aAndb from tablename GROUP BY aAndb ) t
)

只是笔记