java.sql.SQLException: 列名无效

Question

表单添加的时候数据库能正常添加这一行,但是控制台上还是会报 java.sql.SQLException: 列名无效 这个错误?请问怎么回事啊~~~急

//插入方法
public void insert(HttpServletRequest request, HttpServletResponse response) throws ClassNotFoundException, SQLException{
Connection conn=null;
Statement stat=null;
String id=request.getParameter("userid");
String name=request.getParameter("username");
String userage=request.getParameter("age");
String gender=request.getParameter("gender");
conn=connect();
stat=conn.createStatement();
stat.execute("insert into userinfos(userid,username,sex,age) values("+id+",'"+name+"','"+gender+"',"+userage+")");
close(stat,conn);
}