检查重复记录
select count(f_uid) num, f_uid from t_crm_user
group by f_uid having count(f_uid) > 1
order by num desc
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删除重复记录并保留id最大的一条记录
DELETE FROM t_crm_user where f_uid IN (
    SELECT f_uid from (
        SELECT f_uid FROM t_crm_user GROUP BY f_uid HAVING count(f_uid) > 1
    ) a
) AND id NOT IN (
    SELECT keepId FROM (
        SELECT max(id) keepId FROM t_crm_user GROUP BY f_uid HAVING count(f_uid) > 1
    ) b
)
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获取分组后每组的前三条数据
Mysql
-- 效率比较慢
select a.*
from
(
select t1.*,(select count(*)+1 from 表 where 分组字段=t1.分组字段 and 排序字段<t1.排序字段) as group_id
from 表 t1
) a
where a.group_id<=3
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Oracle
SELECT t.*         
   FROM (SELECT ROW_NUMBER() OVER(PARTITION BY 分组字段 ORDER BY 排序字段 DESC) rn,         
         b.*         
         FROM 表 b) t         
  WHERE t.rn <= 3  ;
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【转载，仅作分享，侵删】
作者：storm_fury
来源：CSDN
原文：https://blog.csdn.net/weixin_43215250/article/details/84336007
版权声明：本文为博主原创文章，转载请附上博文链接！

加油，感谢分享