如何在选择下拉列表中选择ID类别？

I have a database table which has all the projects listed in here with a column named "projCat" which is an ID field that relates to another table called projectcats.

The projects table projCat has an ID which relates to the projectscat ID.

<li class="field"><h2>Select Project Sector?</h2>
<select name="projCat" id="projCat" class="input">
<?php 
    $cat = $_GET['cat'];
    $query1 = mysql_query("SELECT * FROM projectscat");

    $checked == '$cat' ? 'selected' : '';

    while($row1 = mysql_fetch_object($query1)){
        echo "<option value=\"" . $row1->projCatID . "\"" . $checked . ">" . $row1->projCatTitle . "</option>
";
    }
?>
</select></li>

The outcome I would like to have is a list of all the project categories but get the projCat so it highlights this category first.

Try this:

    <li class="field"><h2>Select Project Sector? <?php echo $row->projCat;?></h2>
    <select name="projCat" id="projCat" class="input">
    <?php 
        $cat = $_GET['cat'];
        $query1 = mysql_query("SELECT * FROM projectscat");
        while($row1 = mysql_fetch_object($query1)){
            echo "<option value='" . $row1->projCatID . "' selected='";

            if($cat == $row1->[your category in table]) {
                echo "selected";
            } else {
                echo '';
            }
            echo "'>" . $row1->projCatTitle . "</option>";
        }
    ?>
    </select></li>

From the code of IamNewbie

while($row1 = mysql_fetch_object($query1)){
     $checked = $cat ? ' selected="selected"' : '';
    echo "<option value='" . $row1->projCatID . "' " . $checked . ">" . $row1->projCatTitle . "</option>";
}