题目：
题目
编写一个 SQL 查询，来删除Customers表中所有重复的电话号码，重复的电话号码只保留 Id 最小 的那个。
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请至少使用两种方法解答
参考答案：
数据库版本：Server version: 8.0.20 MySQL Community Server - GPL
建表语句
create table dailytest_20200522
(
id int,
phone bigint
);
数据准备
insert into dailytest_20200522 values(1,13512345678);
insert into dailytest_20200522 values(2,13512345678);
insert into dailytest_20200522 values(3,15012345678);
方法1
delete
from dailytest_20200522
where id in (
select A.id
from (
select id, phone, row_number() over (partition by phone order by id ) as cn from dailytest_20200522) A
where A.cn <> 1);
方法2
#通过创建临时表，写入去重后数据，再插入原表
create temporary table dailytest_20200522_temp as select * from dailytest_20200522 where 1=2;
insert into dailytest_20200522_temp select A.id,A.phone
from (
select id, phone, row_number() over (partition by phone order by id ) as cn from dailytest_20200522) A
where A.cn = 1;
truncate table dailytest_20200522;
insert into dailytest_20200522 select * from dailytest_20200522_temp;
drop temporary table dailytest_20200522_temp;
