sql 查詢 某字段是否重復

        select count(*) from
        (
            select * from 客戶 
        )C
        GROUP BY 
        客戶編碼

 

    select * from
    (
        select count(*)num from (
            select 工號,生產線,姓名 from  Base移動用戶
        ) C group by 工號

    )C where num >1