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Mysql中 unique列插入重复值该怎么解决呢_MySQL

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Release: 2016-05-30 17:10:38
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当unique列在一个UNIQUE键上插入包含重复值的记录时,我们可以控制MySQL如何处理这种情况:使用IGNORE关键字或者ON DUPLICATE KEY UPDATE子句跳过INSERT、中断操作或者更新旧记录为新值。

mysql> create table menus(id tinyint(4) not null auto_increment, 
  -> label varchar(10) null,url varchar(20) null,unique key(id)); 
Query OK, 0 rows affected (0.13 sec) 
mysql> insert into menus(label,url) values('Home','home.html'); 
Query OK, 1 row affected (0.06 sec) 
mysql> insert into menus(label,url) values('About us','aboutus.html'); 
Query OK, 1 row affected (0.05 sec) 
mysql> insert into menus(label,url) values('Services','services.html'); 
Query OK, 1 row affected (0.05 sec) 
mysql> insert into menus(label,url) values('Feedback','feedback.html'); 
Query OK, 1 row affected (0.05 sec) 
mysql> select * from menus; 
+----+----------+---------------+ 
| id | label  | url     | 
+----+----------+---------------+ 
| 1 | Home  | home.html  | 
| 2 | About us | aboutus.html | 
| 3 | Services | services.html | 
| 4 | Feedback | feedback.html | 
+----+----------+---------------+ 
4 rows in set (0.00 sec) 
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如果现在在unique列插入一条违背唯一约束的记录,MySQL会中断操作,提示出错:

mysql> insert into menus(id,label,url) values(4,'Contact us','contactus.html'); 
ERROR 1062 (23000): Duplicate entry '4' for key 'id' 
Copy after login

在前面的INSERT语句添加IGNORE关键字时,如果认为语句违背了唯一约束,MySQL甚至不会尝试去执行这条语句,因此,下面的语句不会返回错误:

mysql> insert ignore into menus(id,label,url) values(4,'Contact us','contactus.html'); 
Query OK, 0 rows affected (0.00 sec) 
mysql> select * from menus; 
+----+----------+---------------+ 
| id | label  | url     | 
+----+----------+---------------+ 
| 1 | Home  | home.html  | 
| 2 | About us | aboutus.html | 
| 3 | Services | services.html | 
| 4 | Feedback | feedback.html | 
+----+----------+---------------+ 
4 rows in set (0.00 sec) 
Copy after login

当有很多的INSERT语句需要被顺序地执行时,IGNORE关键字就使操作变得很方便。使用它可以保证不管哪一个INSERT包含了重复的键值,MySQL都回跳过它(而不是放弃全部操作)。

在这种情况下,我们还可以通过添加MySQL4.1新增加的ON DUPLICATE KEY UPDATE子句,使MySQL自动把INSERT操作转换为UPDATE操作。这个子句必须具有需要更新的字段列表,这个列表和UPDATE语句使用的列表相同。

mysql> insert into menus(id,label,url) values(4,'Contact us','contactus.html') 
  -> on duplicate key update label='Contact us',url='contactus.html'; 
Query OK, 2 rows affected (0.05 sec) 
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在这种情况下,如果MySQL发现表已经包含具有相同唯一键的记录,它会自动更新旧的记录为ON DUPLICATE KEY UPDATE从句中指定的新值:

mysql> select * from menus; 
+----+------------+----------------+ 
| id | label   | url      | 
+----+------------+----------------+ 
| 1 | Home   | home.html   | 
| 2 | About us | aboutus.html | 
| 3 | Services | services.html | 
| 4 | Contact us | contactus.html | 
+----+------------+----------------+ 
4 rows in set (0.01 sec) 
Copy after login

以上内容是小编给大家介绍的Mysql中 unique列插入重复值该怎么解决的全部教程,希望对大家有所帮助。

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