给定一个user表，包含id和uid两列，其中uid列可能有重复，要求找出重复的记录，并删掉多余的记录，使得对于uid重复的记录只保留id最小的记录

drop table if EXISTS `tmp`;
create table tmp as select min(id) as id,uid from user GROUP by uid HAVING count(uid)>1;
delete from user where id not in (select id from tmp)  and uid in(select uid from tmp); 
drop table tmp;
commit;

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