databinding system.data.datarowview不包括名为uid的属性，我的数据库的表里有这个字段，控件也加了对应的，代码如下，求大神解答

databinding system.data.datarowview不包括名为uid的属性，我的数据库的表里有这个字段，控件也加了对应的，代码如下，求大神解答SqlConnection   conn=newSqlConnection();        conn.ConnectionString = @"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\mydb.mdf;Integrated Security=True";      
  string SqlStr = "select uid as 学号,uname as 姓名,usex as 性别,math as 数学,chs as语文,en as英语 from grade";        SqlDataAdapter da = new SqlDataAdapter(SqlStr,conn);        DataTable dt = new DataTable();        da.Fill(dt);       
GridView1.Caption = "<b></h2>曙光学校学生成绩表</h2><b>";        GridView1.DataSourceID = null;        GridView1.DataSource = dt;        GridView1.DataBind()
控件代码如下
 <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="uid" DataSourceID="SqlDataSource1">            <Columns>                <asp:BoundField DataField="uid" HeaderText="uid" ReadOnly="True" SortExpression="uid" />                <asp:BoundField DataField="uname" HeaderText="uname" SortExpression="uname" />                <asp:CheckBoxField DataField="usex" HeaderText="usex" SortExpression="usex" />                <asp:BoundField DataField="math" HeaderText="math" SortExpression="math" />                <asp:BoundField DataField="chs" HeaderText="chs" SortExpression="chs" />                <asp:BoundField DataField="en" HeaderText="en" SortExpression="en"/>            </Columns>        </asp:GridView >    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="uid" DataSourceID="SqlDataSource1">            <Columns>                <asp:BoundField DataField="uid" HeaderText="uid" ReadOnly="True" SortExpression="uid" />                <asp:BoundField DataField="uname" HeaderText="uname" SortExpression="uname" />                <asp:CheckBoxField DataField="usex" HeaderText="usex" SortExpression="usex" />                <asp:BoundField DataField="math" HeaderText="math" SortExpression="math" />                <asp:BoundField DataField="chs" HeaderText="chs" SortExpression="chs" />                <asp:BoundField DataField="en" HeaderText="en" SortExpression="en"/>            </Columns>        </asp:GridView >