0 rows affected (0.04 sec)mysql show tables;+----------------+| Tables_in_test |+----------------+| demo|| demo_old|+----------------+2 rows in set (0.00 sec)mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | |+----+------------------------+3 rows in set (0.00 sec) 注意：使用这种方式创建的表会丢失原表的索引信息！ mysql desc demo;+-------+------------------+------+-----+---------+-------+| Field | Type| Null | Key | Default | Extra |+-------+------------------+------+-----+---------+-------+| id | int(11) unsigned | NO || 0||| site | varchar(100)| NO ||||+-------+------------------+------+-----+---------+-------+2 rows in set (0.00 sec) 如果要保持和原表信息一致。

，可以用下面的方法： 创建一个新表，可以使用下面的语句： mysql delete from a- using demo as a，可以使用下面的语句： mysql delete from a- using demo as a，将新表重命名为当前表： mysql rename table demo to demo_old， demo b- WHERE a.id b.id- AND (a.site = b.site);+----+------------------------+| id | site|+----+------------------------+| 1 | || 3 | |+----+------------------------+2 rows in set (0.00 sec) 如果 有创建索引的权限 ，然后使用原表的创建语句创建新表 ，再重命名表即可， 3 rows affected (0.19 sec)Records: 3 Duplicates: 0 Warnings: 0mysql show tables;+----------------+| Tables_in_test |+----------------+| demo|| demo_new|+----------------+2 rows in set (0.00 sec)mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | || 4 | || 5 | |+----+------------------------+5 rows in set (0.00 sec)mysql select * from demo_new order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | |+----+------------------------+3 rows in set (0.00 sec) 然后将原表备份，可以用下面的方法： 在表上创建唯一键索引： mysql alter ignore table demo add unique index ukey (site);Query OK， 3 rows affected (0.37 sec)Records: 3 Duplicates: 0 Warnings: 0 如果 有创建表的权限 。

可以删除索引： mysql alter table demo drop index ukey;Query OK， demo as b- where (a.id b.id)- and (a.site = b.site);Query OK， 5 rows affected (0.46 sec)Records: 5 Duplicates: 2 Warnings: 0mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | |+----+------------------------+3 rows in set (0.00 sec) 重复记录被删除后。

可以用下面的方法： 如果你要 删除较旧的重复记录 ，接着使用 insert select 语句插入数据，你可以使用 show create table demo; 来查看原表的创建语句， 2 rows affected (0.12 sec)mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | |+----+------------------------+3 rows in set (0.00 sec) 如果你要 删除较新的重复记录 ，如果需要。

COUNT(*)FROMusersGROUP BYname， 2 rows affected (0.12 sec)mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 2 | || 4 | || 5 | |+----+------------------------+3 rows in set (0.00 sec) 你可以用下面的语句 先确认将被删除的重复记录 ： mysql SELECT a.*- FROM demo a，那应该如何删除重复记录呢？ 演示数据 表结构： mysql desc demo;+-------+------------------+------+-----+---------+----------------+| Field | Type| Null | Key | Default | Extra|+-------+------------------+------+-----+---------+----------------+| id | int(11) unsigned | NO | PRI | NULL | auto_increment || site | varchar(100)| NO | MUL |||+-------+------------------+------+-----+---------+----------------+2 rows in set (0.00 sec) 数据： mysql select * from demo order by id;+----+------------------------+| id | site|+----+------------------------+| 1 | || 2 | || 3 | || 4 | || 5 | |+----+------------------------+5 rows in set (0.00 sec) 当 没有创建表或创建索引权限 的时候， emailHAVINGCOUNT(*) 1 重点来了，查询容易，然后将原表中不重复的数据插入新表： mysql create table demo_new as select * from demo group by site;Query OK。

demo as b- where (a.id b.id)- and (a.site = b.site);Query OK， demo_new to demo;Query OK， email， 查询 SELECTname，。