列名id无效的异常

列名id无效的错误
public void bind()
  {
  string id = Session["user_id"].ToString();
  string sqlstr = "select * from Users,Roles where Users.user_id = Roles.user_id and Users.user_id = id";

  sqlcon = new SqlConnection(strCon);

  SqlDataAdapter myda = new SqlDataAdapter(sqlstr, sqlcon);

  DataSet myds = new DataSet();

  sqlcon.Open();

  myda.Fill(myds, "table"); 此行出现列名id无效的错误

  GridView1.DataSource = myds;
  GridView1.DataKeyNames = new string[] { "user_id" };//主键

  GridView1.DataBind();

  sqlcon.Close();

  }


------解决方案--------------------------------------------------------
SQL查询字符串写错了，以后记得细心~~

C# code

  string sqlstr = "select * from Users,Roles where Users.user_id = Roles.user_id and Users.user_id = id";改为：  string sqlstr =string.Format( "select * from Users,Roles where Users.user_id = Roles.user_id and Users.user_id = {0} ",  id);