zoukankan      html  css  js  c++  java
  • [LeetCode#182]Duplicate Emails

    Write a SQL query to find all duplicate emails in a table named Person.
    
    +----+---------+
    | Id | Email   |
    +----+---------+
    | 1  | a@b.com |
    | 2  | c@d.com |
    | 3  | a@b.com |
    +----+---------+
    For example, your query should return the following for the above table:
    
    +---------+
    | Email   |
    +---------+
    | a@b.com |
    +---------+
    Note: All emails are in lowercase.
    

    本题是找表Person中重复的邮箱,并且该表中的邮箱字母都是小写字母。这道题比较简单,主要涉及到的知识点就是group by 与 having count 的组合,具体的解法如下:

    解法一:

    SELECT Email from person GROUP BY Email HAVING COUNT(Email)>1;
    

    解法二:

      我们可以使用内交来做,用Email来内交两个表,然后返回Id不同的行,则说明两个不同的人使用了相同的邮箱:

    SELECT DISTINCT p1.Email FROM person p1 
    JOIN person p2 on p1.Email = p2.Email
    WHERE p1.Id <> p2.Id;
    
                  
    申明:本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。
  • 相关阅读:
    禅道安装
    logstash将配置写在多个文件
    原版Filebeat+ELK
    Filebeat+ELK部署文档
    A-2---Jenkins安装
    Linux ftp服务器搭建
    linux 网络命令
    yum安装时出现No more mirrors to try.
    kvm 修改虚拟机密码
    NFS安装
  • 原文地址:https://www.cnblogs.com/lsyb-python/p/11079416.html
Copyright © 2011-2022 走看看