Mysql中 unique列插入重复值该怎么解决呢

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) 

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

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) 

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) 

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)