Parent child Relationship in mysql - php

Question

I am having a table like the following,need to display as Parent and child format
--------------------------------------------------------
id role_name role_id parent_id
--------------------------------------------------------
1 NSM 1 0
2 MR 5 2
3 ASM 4 3
4 ZSM 3 4
5 RSM 2 1
---------------------------------------------------------
the result is like to be the following
NSM
---RSM
-----ZSM
-----NSM
-----MR
NSM->ROOT
RSM->FIRST CHILD
ZSM->SECOND CHILD
NSM->THIRD CHILD
MR->LEAF

Answer 1

// Fetch all the roles
$result = mysql_query("select * from roles");
$roles = array();
while( $role = mysql_fetch_assoc($result) ) {
$roles[] = $role;
}
// Function that builds a tree
function build_tree($roles, $parent_id=0) {
$tree = array();
foreach ($roles as $role) {
if ($role['parent_id'] == $parent_id) {
$tree[] = array(
'role' => $role,
'children' => build_tree($roles, $role['parent_id'])
);
}
}
return $tree;
}
// Function that walks and outputs the tree
function print_tree($tree) {
if (count($tree) > 0) {
print("<ul>");
foreach($node in $tree) {
print("<li>");
htmlspecialchars($node['role']['role_name']);
print_tree($node['children']);
print("</li>");
}
print("</ul>");
}
}

Answer 2

SQL Results are always flat - you'll not be able to return a hierarchy view of that data in a query.
Instead, I would suggest using whichever client components you are using to show that (is it a tree? what exactly?) that knows how to go thru a flat list and build a hierarchy out of that.

Answer 3

If you want to print a view like that in a console (why would you ever want to do that?), you could do like this:
$data = array();
$query = mysql_query("SELECT * FROM table ORDER BY parent_id");
while($array = mysql_fetch_assoc($query))
{
$data[$array['parent_id']][] = $array;
}
function output_hierarchy($id, $prepend)
{
$current = $data[$id];
foreach($current as $item)
{
print $prepend . " " . $item['role_name'];
if(count($data[$item['id']]) > 0)
{
output_hierarchy($item['id'], $prepend . "--");
}
}
}
output_hierarchy(0, '');
If you want to use this on your website, you can easily adapt it. Code should be self-explanatory.