COALESCE Statement working v.good in query window but cannot fill GridView

See more:

C#

ASP.NET

SQL-Server

, +

I have Search Panel with TextBox and Two DropDownList (txtKeyword, ddlCategory, ddlProvider), i want search with one of them or two together or all, so i used COALESCE Statement..

(
	@Course NVARCHAR(200) = NULL,
	@Category NVARCHAR(50) = NULL,
	@Provider NVARCHAR(200) = NULL	
)
AS
BEGIN
SELECT Course.CourseId, Course.CourseName, Course.CourseDescription, 
       Course.CourseHours, Category.CategoryName, Provider.ProviderName, 
       CourseType.CourseTypeName
FROM Course INNER JOIN
     Category ON Course.CategoryId = Category.CategoryId INNER JOIN
     Provider ON Course.ProviderId = Provider.ProviderId INNER JOIN
     CourseType ON Course.CourseTypeId = CourseType.CourseTypeId
WHERE (Course.CourseName = COALESCE (@Course, Course.CourseName)) AND
      (Category.CategoryName = COALESCE (@Category, Category.CategoryName)) AND
      (Provider.ProviderName = COALESCE (@Provider, Provider.ProviderName))

END	

-------------------------------------------------------
Then used it with SqlDataSource and GridView

<asp:GridView ID="gvUserSearch" runat="server" DataKeyNames="CourseID"
        Width="100%" AllowPaging="True" EnableViewState="False"
        AutoGenerateColumns="False">


    <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />

    <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
    <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
    <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
        <Columns>
            <asp:BoundField DataField="CourseID" HeaderText="Course ID" />
            <asp:BoundField DataField="CourseName" HeaderText="Name" />
            <asp:BoundField DataField="CourseDescription" HeaderText="Description" />
            <asp:BoundField DataField="CourseHours" HeaderText="Hours" />
            <asp:BoundField DataField="CategoryName" HeaderText="Category" />
            <asp:BoundField DataField="ProviderName" HeaderText="Provider" />
            <asp:BoundField DataField="CourseTypeName" HeaderText="Course Type" />
        </Columns>
    <EditRowStyle BackColor="#999999" />
    <AlternatingRowStyle BackColor="White" ForeColor="#284775" />

    </asp:GridView>


    <asp:SqlDataSource ID="dsCourses" runat="server"
            ConnectionString="<%$ ConnectionStrings:ShareCon %>" SelectCommand="sp_GetAllCourses"
            SelectCommandType="StoredProcedure">


    <SelectParameters>
        <asp:QueryStringParameter ConvertEmptyStringToNull="true" Name="Course"
        Type="String" QueryStringField="CourseName" />
        <asp:QueryStringParameter ConvertEmptyStringToNull="true" Name="Category"
        Type="String" QueryStringField="Category" />
        <asp:QueryStringParameter ConvertEmptyStringToNull="true" Name="Provider"
        Type="String" QueryStringField="Provider" />
    </SelectParameters>

</asp:SqlDataSource>

--First-- in Main Page that contains (TextBox and DropDownLists only) (there's six states this one of them)

Response.Redirect("SearchResults/Default.aspx?CourseName=" +
                    "&Category=" + "&Provider=");

i tried this too..

Response.Redirect("SearchResults/Default.aspx?CourseName=NULL" +
                    "&Category=NULL" + "&Provider=NULL");

--nd-- in Default.aspx

gvUserSearch.DataSourceID = "dsCourses";
gvUserSearch.DataBind();