how i hinder jquery selector including nested elements?

i'm new jquery hopefully there an easy answer this.

i have html identical to:

<table id="datatable">
    <tr> <!-- i wish quarrel -->
        <td>...</td>
    <tr>
    <tr>
        <td>
           <table>
               <tr> <!-- i wish quarrel -->
                   <td>...</td>
               </tr>
           </table>
        </td>
    <tr>
</table>

i am controlling jquery identical this:

$("#datatable tr").length;

i design length equal 2, nonetheless the returning 3 (includes <tr> nested table.) doubt is: i hinder 3rd <tr> being selected?

i know i supplement an ignorethisrow category final quarrel bar results, nonetheless i'd move an choice allows me control depth name engine searches.