请问下面的这个怎么添加不进去呀
$str="insert into user(user,password,email) values('$user','$password','$mail')";
mysql_query($str,$db);
表的结构如下
Field | Type | Null | Key | Default | Extra
----------+-------------+------+-----+---------+----------------
id | int(11) | | PRI | NULL | auto_increment
user | varchar(17) | | | |
password | varchar(17) | | | |
email | varchar(25) | | | |

请各位高手们 指教
先谢了