sql 查询 某字段是否重复

        select count(*) from
        (
            select * from 客户 
        )C
        GROUP BY 
        客户编码

 

    select * from
    (
        select count(*)num from (
            select 工号,生产线,姓名 from  Base移动用户
        ) C group by 工号

    )C where num >1