数据库插入不进去！！

<%@ page contentType="text/html;charset=GB2312" import="java.sql.*,java.util.*"%>
<jsp:useBean id="db" scope="page" class="BookShop.MyDb"></jsp:useBean>
<%request.setCharacterEncoding("gb2312");%>
<%

//获取注册数据
String id=(String)request.getParameter("id");
String username=(String)request.getParameter("username");
String password=(String)request.getParameter("password");
String realname=(String)request.getParameter("realname");
String email=(String)request.getParameter("email");
//String phone=(String)request.getParameter("phone");
String phone=(String)request.getParameter("phone");
String zip=(String)request.getParameter("zip");
String address=(String)request.getParameter("address");
String sql="insert into customers values ('lcx198625','fds','987','刘','654@163.com',321654,063000,'河北')";
//String sql="insert into customers(idcustomer,username,password，realname,email,phone,zip,address) values('"+id+"','"+username+"','"+password+"','"+realname+"','"+email+"','"+phone+"','"+zip+"','"+address+"')";
db.update(sql);

%>

<html>
<head>
<title>会员注册</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
</head>
<body>

id是<%=id%>
<br>
用户名<%=username%>
<br>
密码是<%=password%>
<br>
真实姓名是<%=realname%>
<br>
email是<%=email%>
<br>
电话是<%=phone%>
<br>
邮编是<%=zip%>
<br>
地址是<%=address%>
<br>
</body>
</html>

上面是我的程序,就是在插入数据库那段,插不进去
不过,要是插入常量就可以
例如String sql="insert into customers values ('lcx198625','fds','987','刘','654@163.com',321654,063000,'河北')";
db.update(sql);
但是一变成变量就插不进去
而且从上一页接收变量一切正常
大家帮我看看 谢谢了