Forms Data Controls :: Multiple Dropdown Filters To Sort A Grid View

wondering if someone can possibly help me out with a gridview. I have data coming into a grid and I know how to filter the data using one dropdown, I'm trying to get a little more advanced now. I'd like to filter using three dropdowns.

This is what I have so far: I don't know how to hook the downlists to the query?

<asp:DropDownList runat="server" id="DropDownList1" Width="90px">
<asp:ListItem Value="item_num">Item #</asp:ListItem>
<asp:ListItem Value="lot_num">Lot #</asp:ListItem>
<asp:ListItem Value="production_code">Production Code
</asp:ListItem>
<asp:ListItem Value="batchcode">Batch Code</asp:ListItem>
<asp:ListItem Value="inbound_no">Inbound #</asp:ListItem>
<asp:ListItem Value="recv_date">Received Date</asp:ListItem>
<asp:ListItem Value="location">Location</asp:ListItem>
<asp:ListItem Value="category">Category</asp:ListItem>
</asp:DropDownList>
<asp:DropDownList runat="server" id="DropDownList2" Width="160px">
<asp:ListItem Value="=">is equal to</asp:ListItem>
<asp:ListItem Value="<=">is less than or equal to
</asp:ListItem>
<asp:ListItem Value=">=">is greater than or equal to
</asp:ListItem>
<asp:ListItem Value="<>">is not equal to</asp:ListItem>
<asp:ListItem Value="begins with">Begins With</asp:ListItem>
<asp:ListItem Value="Like">Ends With</asp:ListItem>
</asp:DropDownList>
<asp:TextBox runat="server" id="TextBox1" Width="150px">
</asp:TextBox>
<asp:Button runat="server" Text="Go" id="Button8" BackColor="Lime" />
<asp:Button runat="server" Text="Clear Filter" id="Button9" /><br />
<input name="Checkbox1" type="checkbox" /><label id="Label5">
Include Items containing "Zero on Hand" Quantity.<br />
Group by Fields: <input name="Checkbox2" type="checkbox" />
Item/Lot
<input name="Checkbox3" type="checkbox" /> Production Code
<input name="Checkbox4" type="checkbox" /> Batch Code</label><label id="Label4"></label><br />
<hr />
<asp:GridView runat="server" id="GridView1" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" Font-Size="Small" BorderStyle="None" BackColor="White" GridLines="Vertical" BorderColor="#999999" BorderWidth="1px" CellPadding="3" Font-Underline="False"
AllowSorting="True" AllowPaging="True" PageSize="20">
<RowStyle BackColor="#EEEEEE" ForeColor="Black" />
<Columns>
<asp:boundfield DataField="STATUS" HeaderText="Status" SortExpression="STATUS">
</asp:boundfield>
<asp:boundfield DataField="ITEM_NUM" HeaderText="Item #" SortExpression="ITEM_NUM">
</asp:boundfield>
<asp:boundfield DataField="LOT_NUM" HeaderText="Lot #" SortExpression="LOT_NUM">
</asp:boundfield>
<asp:boundfield DataField="LOT_EXT" HeaderText="Lot Ext" SortExpression="LOT_EXT">
</asp:boundfield>
<asp:boundfield DataField="RECV_DATE" HeaderText="Recv Dt" SortExpression="RECV_DATE">
</asp:boundfield>
<asp:boundfield DataField="PRODUCTION_CODE" HeaderText="Prod Code" SortExpression="PRODUCTION_CODE">
</asp:boundfield>
<asp:boundfield DataField="QTY_ONHAND" DataFormatString="{0:NO}" HeaderText="OnHand" SortExpression="QTY_ONHAND">
</asp:boundfield>
<asp:boundfield DataField="QTY_RESERV" HeaderText="Reserv" SortExpression="QTY_RESERV">
</asp:boundfield>
<asp:boundfield DataField="QTY_AVAIL" DataFormatString="{0:N}" HeaderText="Avail" SortExpression="QTY_AVAIL">
</asp:boundfield>
<asp:boundfield DataField="QTY_ADJUST" HeaderText="Adjust" SortExpression="QTY_ADJUST">
</asp:boundfield>
<asp:boundfield DataField="QTY_SHIP" HeaderText="Shipped" SortExpression="QTY_SHIP">
</asp:boundfield>
<asp:boundfield DataField="QTY_RECV" HeaderText="Recv" SortExpression="QTY_RECV">
</asp:boundfield>
<asp:boundfield DataField="PROD_DATE" HeaderText="Prod Date" SortExpression="PROD_DATE">
</asp:boundfield>
<asp:boundfield DataField="RELEASE_DATE" HeaderText="Release" SortExpression="RELEASE_DATE">
</asp:boundfield>
</Columns>
<FooterStyle BackColor="#CCCCCC" ForeColor="Black" />
<PagerStyle HorizontalAlign="Center" BackColor="#999999" ForeColor="Black" />
<SelectedRowStyle BackColor="#008A8C" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#000084" ForeColor="White" Font-Bold="True" />
<AlternatingRowStyle BackColor="#DCDCDC" />
</asp:GridView>
<asp:SqlDataSource runat="server" id="SqlDataSource1" ConnectionString="<%$ ConnectionStrings:RemoteRooster %>" SelectCommand="SELECT * FROM [INVENTRY] WHERE OWNER = 'CompanyName' AND QTY_ONHAND > '0'">
</asp:SqlDataSource>