我正在尝试编写一个层次结构检测脚本，我已经编写了该脚本，但是只能下降4级。有没有一种方法可以将其压缩为几行，并且可以使用无数个关卡？

这个脚本基本上是相同的代码复制并粘贴4次

<?php
function listCategories($name, $disable_status = 0, $show_nums = 0) {
    echo "<select name='".$name."'>";
    $result = mysql_query("SELECT * FROM categories") or die(mysql_error());
    while($row = mysql_fetch_array($result)) {
        if($row['parent_id']==0) {
            $result2 = mysql_query("SELECT * FROM categories WHERE parent_id=".$row['id']) or die(mysql_error());
            echo "<option value='".$row['id']."'";

            if($disable_status==1&&isParent($row['id'])){
                echo " disabled='disabled'";
            }
            echo ">".$row['name']."</option>";

            while($row2 = mysql_fetch_array($result2)) {
                $result3 = mysql_query("SELECT * FROM categories WHERE parent_id=".$row2['id']) or die(mysql_error());
                echo "<option value='".$row2['id']."'";
                if($disable_status==1&&isParent($row2['id'])){
                    echo " disabled='disabled'";
                }
                echo ">- ".$row2['name']."</option>";

                while($row3 = mysql_fetch_array($result3)) {
                    $result4 = mysql_query("SELECT * FROM categories WHERE parent_id=".$row3['id']) or die(mysql_error());
                    echo "<option value='".$row3['id']."'";
                    if($disable_status==1&&isParent($row3['id'])){
                        echo " disabled='disabled'";
                    }
                    echo ">-- ".$row3['name']."</option>";

                    while($row4 = mysql_fetch_array($result4)) {
                        echo "<option value='".$row4['id']."'>[".$row4['id']."] --- ".$row4['name']."</option>";
                    }
                }
            }
        }
    }
    echo "</select>";
}

function isParent($cat_ID) {
    $result = mysql_query("SELECT * FROM categories WHERE parent_id=".$cat_ID) or die(mysql_error());
    if(mysql_num_rows($result)==0) {
        return FALSE;
    } else {
        return TRUE;
    }
}

我的表结构categories是

id, name, parent_id

如果类别没有父类别，parent_id则将为0，否则将为id其父类别的。

感谢所有帮助。