mysql删除数据库重复记录达成方法
发布时间：2022-06-15 13:39:42 所属栏目：MySql教程 来源：互联网
导读：文章详细的利用了一个实例来告诉我们如何在mysql删除数据库重复记录的实现方法与原理,有需要的同学可以参考一下. 演示数据,表结构,代码如下: mysql desc demo; +-------+------------------+------+-----+---------+----------------+ | Field | Type | Null
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文章详细的利用了一个实例来告诉我们如何在mysql删除数据库重复记录的实现方法与原理,有需要的同学可以参考一下. 演示数据,表结构,代码如下: 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 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | | 4 | http://www.phpfensi.com | | 5 | http://www.phpfensi.com | +----+------------------------+ 5 rows in set (0.00 sec) 当没有创建表或创建索引权限的时候,如果你要删除较旧的重复记录,可以使用下面的语句: mysql> delete from a -> using demo as a, demo as b -> where (a.id > b.id) -> and (a.site = b.site); Query OK, 2 rows affected (0.12 sec) mysql> select * from demo order by id; +----+------------------------+ | id | site | +----+------------------------+ | 1 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | +----+------------------------+ 3 rows in set (0.00 sec) 你要删除较新的重复记录,可以使用下面的语句: mysql> delete from a -> using demo as a, demo as b -> where (a.id < b.id) -> and (a.site = b.site); Query OK, 2 rows affected (0.12 sec) mysql> select * from demo order by id; +----+------------------------+ | id | site | +----+------------------------+ | 2 | | | 4 | http://www.phpfensi.com | | 5 | http://www.phpfensi.com | +----+------------------------+ 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,代码如下: mysql> SELECT a.* -> FROM demo a, demo b -> WHERE a.id > b.id -> AND (a.site = b.site); +----+------------------------+ | id | site | +----+------------------------+ | 1 | http://www.phpfensi.com | | 3 | http://www.phpfensi.com | +----+------------------------+ 2 rows in set (0.00 sec) 如果有创建索引的权限,可以用下面的方法,在表上创建唯一键索引,代码如下: mysql> alter ignore table demo add unique index ukey (site); Query OK, 5 rows affected (0.46 sec) Records: 5 Duplicates: 2 Warnings: 0 mysql> select * from demo order by id; +----+------------------------+ | id | site | +----+------------------------+ | 1 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | +----+------------------------+ 3 rows in set (0.00 sec) 重复记录被删除后,如果需要,可以删除索引,代码如下: mysql> alter table demo drop index ukey; Query OK, 3 rows affected (0.37 sec) Records: 3 Duplicates: 0 Warnings: 0 如果有创建表的权限,可以用下面的方法,创建一个新表,然后将原表中不重复的数据插入新表,代码如下: mysql> create table demo_new as select * from demo group by site; Query OK, 3 rows affected (0.19 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> 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 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | | 4 | http://www.phpfensi.com | | 5 | http://www.phpfensi.com | +----+------------------------+ 5 rows in set (0.00 sec) mysql> select * from demo_new order by id; +----+------------------------+ | id | site | +----+------------------------+ | 1 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | +----+------------------------+ 3 rows in set (0.00 sec) 然后将原表备份,将新表重命名为当前表,代码如下: mysql> rename table demo to demo_old, demo_new to demo; Query OK, 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 | http://www.phpfensi.com | | 2 | | | 3 | http://www.phpfensi.com | +----+------------------------+ 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,代码如下: 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,你可以使用 show create table demo;来查看原表的创建语句,然后使用原表的创建语句创建新表,接着使用 insert … select 语句插入数据,再重命名表即可 （编辑：开发网_开封站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
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