ฟังก์ชั่นการกรอง Gridview ในตัว?

<asp:GridView ID="Gridview1" runat="server" AutoGenerateColumns="False" AllowPaging="True"
AllowSorting="true" DataSourceID="dsGridview" Width="650px" PageSize="20"
CssClass="Gridview">
<Columns>
    <asp:BoundField DataField="id" HeaderText="id" SortExpression="id"
        ItemStyle-Width="50px" ItemStyle-HorizontalAlign="Center" />
    <asp:BoundField DataField="FirstName" HeaderText="Sort" SortExpression="FirstName"
        ItemStyle-Width="150px" />
    <asp:BoundField DataField="LastName" HeaderText="Sort" SortExpression="LastName"
        ItemStyle-Width="150px" />
    <asp:BoundField DataField="Department" HeaderText="Sort" SortExpression="Department"
        ItemStyle-Width="150px" />
    <asp:BoundField DataField="Location" HeaderText="Sort" SortExpression="Location"
        ItemStyle-Width="150px" />
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:EvonetConnectionString %>"
SelectCommand="SELECT * FROM [T_Employees]" />

<table style="width: 650px" border="0" cellpadding="0" cellspacing="1"
class="GridviewTable">
<tr>
    <td style="width: 50px;">
        ID
    </td>
    <td style="width: 150px;">
        First Name
    </td>
    <td style="width: 150px;">
        Last Name
    </td>
    <td style="width: 150px;">
        Department
    </td>
    <td style="width: 150px;">
        Location
    </td>
</tr>
<tr>
    <td style="width: 50px;">
    </td>
    <td style="width: 150px;">
    </td>
    <td style="width: 150px;">
    </td>
    <td style="width: 150px;">
        <asp:DropDownList ID="ddldepartment" DataSourceID="dsPopulateDepartment"
            AutoPostBack="true" DataValueField="department" runat="server" Width="130px"
            Font-Size="11px" AppendDataBoundItems="true">
            <asp:ListItem Text="All" Value="%"></asp:ListItem>
        </asp:DropDownList>
    </td>
    <td style="width: 150px;">
        <asp:DropDownList ID="ddlLocation" DataSourceID="dsPopulateLocation"
            AutoPostBack="true" DataValueField="location" runat="server" Width="130px"
            Font-Size="11px" AppendDataBoundItems="true">
            <asp:ListItem Text="All" Value="%"></asp:ListItem>
        </asp:DropDownList>
    </td>
</tr>
<tr>
    <td colspan="5">
        <asp:GridView ID="Gridview1" runat="server" AutoGenerateColumns="False"
            AllowPaging="True" AllowSorting="true" DataSourceID="dsGridview"
            Width="650px" PageSize="10" CssClass="Gridview">
            <Columns>
                <asp:BoundField DataField="id" HeaderText="Sort" SortExpression="id"
                    ItemStyle-Width="50px" ItemStyle-HorizontalAlign="Center" />
                <asp:BoundField DataField="FirstName" HeaderText="Sort"
                    SortExpression="FirstName" ItemStyle-Width="150px" />
                <asp:BoundField DataField="LastName" HeaderText="Sort"
                    SortExpression="LastName" ItemStyle-Width="150px" />
                <asp:BoundField DataField="Department" HeaderText="Sort"
                    SortExpression="Department" ItemStyle-Width="150px" />
                <asp:BoundField DataField="Location" HeaderText="Sort"
                    SortExpression="Location" ItemStyle-Width="150px" />
            </Columns>
        </asp:GridView>
    </td>
</tr>
</table>

.GridviewDiv {font-size: 62.5%; font-family: 'Lucida Grande',
    'Lucida Sans Unicode', Verdana, Arial, Helevetica, sans-serif; color: #303933;}
Table.Gridview{border:solid 1px #df5015;}
.GridviewTable{border:none}
.GridviewTable td{margin-top:0;padding: 0; vertical-align:middle }
.GridviewTable tr{color: White; background-color: #df5015; height: 30px; text-align:center}
.Gridview th{color:#FFFFFF;border-right-color:#abb079;border-bottom-color:#abb079;
    padding:0.5em 0.5em 0.5em 0.5em;text-align:center}
.Gridview td{border-bottom-color:#f0f2da;border-right-color:#f0f2da;
    padding:0.5em 0.5em 0.5em 0.5em;}
.Gridview tr{color: Black; background-color: White; text-align:left}
:link,:visited { color: #DF4F13; text-decoration:none }

<asp:DropDownList ID="ddldepartment" DataSourceID="dsPopulateDepartment"
AutoPostBack="true" DataValueField="department" runat="server" Width="130px" Font-Size="11px"
AppendDataBoundItems="true">
    <asp:ListItem Text="All" Value="%"></asp:ListItem>
</asp:DropDownList>
<asp:SqlDataSource ID="dsPopulateDepartment" runat="server"
ConnectionString="<%$ ConnectionStrings:EvonetConnectionString %>" SelectCommand="SELECT
DISTINCT Department from [T_Employees]"></asp:SqlDataSource>

<asp:SqlDataSource ID="dsGridview" runat="server"
    ConnectionString="<%$ ConnectionStrings:EvonetConnectionString %>"
    SelectCommand="SELECT * FROM [T_Employees]" FilterExpression="Department like '{0}%'
    and Location like '{1}%'">
    <FilterParameters>
        <asp:ControlParameter Name="Department" ControlID="ddldepartment"
            PropertyName="SelectedValue" />
        <asp:ControlParameter Name="Location" ControlID="ddllocation"
            PropertyName="SelectedValue" />
    </FilterParameters>
</asp:SqlDataSource>