delete users_groups as a from users_groups as a,
(
select *,min(id) from users_groups group by uid having count(1) > 1
) as b
where a.uid = b.uid and a.id > b.id;
(
select *,min(id) from users_groups group by uid having count(1) > 1
) as b
where a.uid = b.uid and a.id > b.id;
保留id最小的那个uid值
