借鉴博客：https://www.cnblogs.com/loveufofbi/p/12148988.html
方法一
SELECT * FROM ( SELECT `openid` , COUNT( * ) AS c FROM ing_jf_shop GROUP BY `openid` )t WHERE c >1
方法二
SELECT openid , COUNT(openid) FROM ing_jf_shop GROUP BY openid HAVING COUNT(openid) > 1
-- ing_jf_shop 是表名
-- openid 是要确定是否有重复值的字段