把同个相同字段的表合并成一个表，数据有相同的，把其中一个id最小的删除，留下id最大的一条数据。

delete from member where id in
(
    select a.id from
    (
        select min(id) id from member a where EXISTS
        (
            select 1 from member b where a.mid=b.mid group by mid HAVING count(*)>1
        )
        group by mid
    ) a
)

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