Recursive tree traversal with mysql through PHP - php

Question

I am creating a questionnaire for a client that requires the questions to be organized by 3 layers of levels. I've successfully created the U.I. however I've been trying for the last 3 hours to pull data from a database in such a way that everything loads in the right place. The database is organized like so by the client so I have no control over it:
id description parentId
1 Level 1 0
2 Level 2 0
3 Level 1a 1
4 Level 1b 1
5 Level 1a1 3
I have found a similar question to mine on the site but when I attempted it's solution I got the following on repeat infinetly:
Code:
function makeList($par_id = 0) {
//your sql code here
$result = mysql_query("SELECT * FROM pB_test WHERE parentId = $par_id");
$pages = mysql_fetch_array( $result );
if (count($pages)) {
echo '<ul>';
foreach ($pages as $page) {
echo '<li>', $page['description'];
makeList($page['parentId']);
echo '</li>';
}
echo '</ul>';
}
}
makeList();
Output:
1
3
5
5
l
l
3
5
5
l
l
3
5
5
l
l
3
5
5
l
l
Does anyone know how to fix this and what the issue is exactly? Cheers

Answer 1

it's not good to call mysql server and fetch result each time
what if you have over 100 rows? or 200+
use this to query only once:
$result = mysql_query("SELECT * FROM test");
$arrs = array();
while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
$arrs[] = $row;
}
function build_tree($arrs, $parent_id=0, $level=0) {
foreach ($arrs as $arr) {
if ($arr['parent_id'] == $parent_id) {
echo str_repeat("-", $level)." ".$arr['name']."<br />";
build_tree($arrs, $arr['id'], $level+1);
}
}
}
build_tree($arrs);
common example for table
id name parent_id

Answer 2

Do this recursivly:
function printChildQuestions($parentid) {
$sql="SELECT * FROM pB_test WHERE parentID=$parentid";
$result=mysql_query($sql);
$i=0;
while (true) {
$row=mysql_fetch_array($result);
if (!$row) break;
if ($i==0) echo "<ul>";
$i=1;
echo '<li>'.$row['id'].' '.$row['description'].' '.$row['parentId'].'</li>';
printChildQuestions($row['id']);
}
if ($i>0) echo '</ul>';
}
printChildQuestions(0);