apply filter in repeater control

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C#

ASP.NET

SQL

I have repeater control and i am fetching records from database, so i have number of records and i want to filter my result by using dropdowns. I am using ajax. If i select first dropdown then it filter result according to first and again when i select second dropdown then it fetch result according to second only, but i want if one dropdown is already selected then on selecting second dropdown it should filter from previous dropdown result. How to do it...
My search dropdowns are in master page and among these only category dropdown is compulsory to select and result shows in result.aspx page and also my filter dropdowns are in result page.
master page code:

<asp:DropDownList ID="dd_state" runat="server" CssClass="dropdownstyle2" >
            </asp:DropDownList>

            <asp:TextBox ID="txt_pincode" runat="server" CssClass="dropdownstyle3" value="Pincode" Text="" onKeyUp="numericFilter(this);" maxlength="6"
            onFocus="if(this.value==this.defaultValue) this.value=''; " onBlur="if(this.value=='') this.value=this.defaultValue;"></asp:TextBox>

            <asp:DropDownList ID="dd_category" runat="server" CssClass="dropdownstyle4" 
                AutoPostBack="True" onselectedindexchanged="dd_category_SelectedIndexChanged">
            </asp:DropDownList>

            <asp:DropDownList ID="dd_subcategory" runat="server" CssClass="dropdownstyle5" >
            </asp:DropDownList>

            <asp:Button ID="but_go" runat="server" Text="Go" CssClass="gobuttonstyle" OnClientClick="return validate();" 
                onclick="but_go_Click"/>

    protected void but_go_Click(object sender, EventArgs e)
{
    Session["country"] = 1;
    Session["state"] = dd_state.SelectedValue;
    Session["pincode"]  = txt_pincode.Text;
    Session["category"] = dd_category.SelectedValue;
    Session["subcategory"] = dd_subcategory.SelectedValue;
    Response.Redirect("Results.aspx");
}

Result.aspx.cs

protected void BindRepeaterData()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("sps_searchresult", con);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@country", 1);
        cmd.Parameters.AddWithValue("@state", state);
        cmd.Parameters.AddWithValue("@pincode", pincode);
        cmd.Parameters.AddWithValue("@category", category);
        cmd.Parameters.AddWithValue("@subcategory", subcategory);
        
        DataSet ds = new DataSet();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        da.Fill(ds);
        rep_results.DataSource = ds;
        rep_results.DataBind();
        con.Close();
    }

ALTER PROCEDURE [dbo].[sps_searchresult]
	@country nvarchar(10),
	@state nvarchar(20),
	@pincode nvarchar(10),
	@category nvarchar(10),
	@subcategory nvarchar(20)
	
AS
BEGIN
	
	if(@state='Select State' and @pincode='Pincode' and @subcategory='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category
	end
	
	if(@state='Select State' and @pincode='Pincode' and @subcategory!='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and subcategory=@subcategory
	end
	
	if(@state='Select State' and @pincode!='Pincode' and @subcategory='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and pincode=@pincode
	end
	
	if(@state='Select State' and @pincode!='Pincode' and @subcategory!='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and pincode=@pincode and subcategory=@subcategory
	end
	
	if(@state!='Select State' and @pincode='Pincode' and @subcategory='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and state=@state
	end
	
	if(@state!='Select State' and @pincode='Pincode' and @subcategory!='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and state=@state and subcategory=@subcategory
	end
	
	if(@state!='Select State' and @pincode!='Pincode' and @subcategory='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and state=@state and pincode=@pincode
	end
	
	if(@state!='Select State' and @pincode!='Pincode' and @subcategory!='Select Sub-Category')
	begin
	select r.*, s.s_name, CASE iam WHEN 1 THEN 'Professional/Business' ELSE 'Individual' End as iamdetail, substring(description,1,200)+'...' AS shortdescription, substring(title,1,40) AS shorttitle from tbl_adregister r INNER JOIN tbl_state s ON r.state = s.s_id 
	where country=@country and category=@category and state=@state and pincode=@pincode and subcategory=@subcategory
	end
	
END

filter dropdowns at result page:

<asp:DropDownList ID="dd_state" runat="server" AutoPostBack="True"
onselectedindexchanged="dd_state_SelectedIndexChanged" ></asp:DropDownList>
<br/>
<asp:DropDownList ID="dd_category" runat="server" AutoPostBack="True"
onselectedindexchanged="dd_category_SelectedIndexChanged"></asp:DropDownList>
<br/>
<asp:DropDownList ID="dd_subcategory" runat="server" AutoPostBack="True"
onselectedindexchanged="dd_subcategory_SelectedIndexChanged"></asp:DropDownList>