php - How do I get rows to correspond to other rows based on a parent_id , all from the same table -

i assuming not easy way of doing , it's home assignment, bear me please.

i have table in mysql 'menu' following structure :

id - number   parent_id - number (0 root)    title - string   link - string   

the parent_id links id of row , in case product1 products.

example :    1 | 0 |    | about.html   2 | 0 | products | products.html   3 | 2 | product1 | product1.html   4 | 2 | product2 | product2.html   5 | 2 | product3 | product3.html   

my goal make set of ul's :

<ul>     <li><a href="about.html"> </a></li>     <li><a href="products.html"> products </a>              <ul>                     <li> <a href="product1.html"> product 1 </a></li>                     <li> <a href="product1.html"> product 1 </a></li>                     ...             </ul>     </li>     ... </ul> 

so far i've made 1 ul :

<?php function getall() {   dbconnect();   $result = mysql_query("select * `menu`");  $listitems = array();   while ($li = mysql_fetch_array($result)) {     $listitems[] = $li;  }  return $listitems;  }  ?> <ul>         <?php         include_once 'functions.php';         $listitems = getall();         foreach ($listitems $listitem) {         ?>             <li><a href="<?php print $listitem['link']; ?>"><?php print   $listitem['title']; ?></a></li>          <?php } ?> </ul> 

this problem starts , can't figure out how make second function or how condition in order "submenu" rows ul in ul.

if don´t have huge number of elements in table it´s easy solve this. syed qarib user said, can check if current item has children´s.

the key make paint of html recursive using parent_id.

this code need:

<?php function getelementsbyparentid($parent_id) {       dbconnect();       $query = sprintf("select * `menu` parent_id=%s",      mysql_real_escape_string($parent_id));       $result = mysql_query($query);               <!-- alternative using concat              $result = mysql_query("select * `menu` parent_id=".$parent_id);              -->      $listitems = array();       while ($li = mysql_fetch_array($result)) {         $listitems[] = $li;      }      return $listitems;  }   function paintchildrens($parent_id) {      $listitems = getelementsbyparentid($parent_id);      if (count($listitems) > 0) {          ?>         <ul>         <?php                foreach($listitems $listitem) {             ?>                 <li><a href="<?php print $listitem['link']; ?>"><?php print   $listitem['title']; ?></a></li>             <?php              paintchildrens($listitem['id']);         }                    ?>         </ul>         <?php     }         }  include_once 'functions.php'; paintchildrens(null) ?> 

i´m not php developer it´s possible code has errors null value check.