Retain Binding

I have below gridview and sqldatasource.

            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="AccountID"
                DataSourceID="SqlDataSource1" AllowPaging="True" PageSize="2" CellPadding="4"
                ForeColor="#333333" GridLines="None" EmptyDataText="No results returned" EnableSortingAndPagingCallbacks="True">
                <Columns>
                    <asp:BoundField DataField="AccountID" HeaderText="AccountID" InsertVisible="False"
                        ReadOnly="True" SortExpression="AccountID" Visible="False" />
                    <asp:BoundField DataField="UserID" HeaderText="User ID" SortExpression="UserID" />
                    <asp:BoundField DataField="FullName" HeaderText="Name" SortExpression="FullName" />
                    <asp:BoundField DataField="Role" HeaderText="Role" SortExpression="Role" />
                    <asp:BoundField DataField="CompanyName" HeaderText="Company" SortExpression="CompanyName" />
                    <asp:BoundField DataField="T1" HeaderText="T1" SortExpression="T1" />
                    <asp:BoundField DataField="T2" HeaderText="T2" SortExpression="T2" />
                    <asp:BoundField DataField="T3" HeaderText="T3" SortExpression="T3" />
                    <asp:BoundField DataField="BT" HeaderText="BT" SortExpression="BT" />
                    <asp:BoundField DataField="Status" HeaderText="Status" SortExpression="Status" />
                </Columns>
                <PagerSettings Position="Top" Mode="NumericFirstLast" />
                <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
                <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
                <EditRowStyle BackColor="#999999" />
                <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
                <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Right" />
                <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
                <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
            </asp:GridView>
            <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:CaasConnectionString %>"
                SelectCommand="Select AccountID, UserID, FullName, Case RoleType When 0 Then 'Admin' Else 'User' End 'Role', t2.CompanyName, Case T1 When 1 Then 'Y' Else 'N' End 'T1', Case T2 When 1 Then 'Y' Else 'N' End 'T2', Case T3 When 1 Then 'Y' Else 'N' End 'T3', Case BT When 1 Then 'Y' Else 'N' End 'BT', Case t1.Status When 1 Then 'Active' Else 'Disabled' End 'Status'
From tblAccount t1 Inner Join tblCompany t2 On t1.CompanyID = t2.CompanyID
Where 1 = 0
Order By UserID"></asp:SqlDataSource>

I also have a submit button. On submit, I will build a sql statement dynamically and rebind the gridview as below.

    protected void btnSearch_Click(object sender, EventArgs e)
    {
///////
        SqlDataSource1.SelectCommand = sql;
        SqlDataSource1.SelectCommandType = SqlDataSourceCommandType.Text;
        GridView1.DataBind();
    }

All works but problem arises when I click on next page index of gridview. I enable paging for my datagrid. On click of another page index, no results is returned by the datasouce. How come?