如何修改代码类别ul li这些代码？

Question

function display_children_category($parent, $level) { 
    $db = new My_sqli();    
    $result ="SELECT parent.product_category_id, parent.product_category_name, parent.product_category_level, count(product.product_name) AS sum_products FROM product_category AS node JOIN product_category AS parent ON node.product_category_lft BETWEEN parent.product_category_lft AND parent.product_category_rgt LEFT JOIN product ON node.product_category_id = product.product_category_id WHERE parent.product_category_parent='$parent' GROUP BY parent.product_category_name, parent.product_category_level ORDER BY node.product_category_lft";

    // display each child 
    $num = $db->get_results($result);

    foreach($num as $row){
             echo "<li>".str_repeat('',$level).$row['product_category_name']."( ".$row['sum_products']." ชิ้น)</li>"; 
             display_children_category($row['product_category_id'], $level+1); 
    }   

} 

How to modify code category ul li form these code? Please help me.

I would like category menu

<ul>  
    <li>test</li>  
    <li>test2</li>  
    <li>test3
        <ul>
            <li>subtest3-1</li>
            <li>subtest3-2</li>
        </ul> 
    </li> 
</ul>

Answer 1

Do not echo directly, instead go with a string containing your li

function display_children_category($parent, $level) { 
    $db = new My_sqli();    
    $result ="SELECT parent.product_category_id, parent.product_category_name, parent.product_category_level, count(product.product_name) AS sum_products FROM product_category AS node JOIN product_category AS parent ON node.product_category_lft BETWEEN parent.product_category_lft AND parent.product_category_rgt LEFT JOIN product ON node.product_category_id = product.product_category_id WHERE parent.product_category_parent='$parent' GROUP BY parent.product_category_name, parent.product_category_level ORDER BY node.product_category_lft";

    // display each child 
    $num = $db->get_results($result);
    $str = '';

    foreach($num as $row){
             $str .= "<li>".str_repeat('',$level).$row['product_category_name']."( ".$row['sum_products']." ชิ้น)"; 
             $str .= display_children_category($row['product_category_id'], $level+1); 
             $str .= "</li>";
    }

    return ($str) ? "<ul>".$str."</ul>" : "";


} 

Then when you call the function in your outside script :

echo display_children_category($param1,$param2);