How to fetch query where sub/child create new UL - php

Question

I am trying to make un-order list for parent child categories where if there is any child category than it will create another un-order list ( like indented text) so user can understand properly.
I have fetch sql but with foreach I don't understand how to set so where child category only will display under parent category by creating another un-order list under the parent category.
Here is my code
$query_cat = "SELECT * FROM ^categories";
$query = qa_db_query_sub($query_cat);
$catsid = qa_db_read_all_assoc($query);
echo '<UL>';
foreach ($catsid as $catid){
echo '<LI>'. $catid['title'].' '. $catid['categoryid'].'</LI>';
}
echo '</UL>';
So final result would be
First Category
Sub Category1
Second Category
EDIT:
After modified code with #vlcekmi3 answer https://stackoverflow.com/a/13451136/1053190 I am getting this result
Now how to exclude subcategory from parent list?

Answer 1

There's no really easy solution for this with your design. The most effective way would be to add column like order_in_list (and maybe depth_in_list).
They would be pre calculated in loop (pseudocode):
START TRANSACTION
UPDATE t1 SET order_in_list = 0 // Restart whole loop
$ids = array(0);
while $id = array_shift($ids){
$record = SELECT * FROM t1 WHERE id = $id // Get id details, order_in_list is important
$children = SELECT * FROM t1 WHERE parent_id = $id // get list of all childs
// If it's root element, start indexing from 0
$root_order = ($record ? $record->order_in_list : 1)
$child_no = count($children) // How many child will be adding
// No children, nothing to do:
if $child_no < 1{
continue;
}
append_to_array($ids, $children) // Store ids to process
// Shift all later records, we'll be creating gap in order_in_list 1,2,3,4,5
// To 1,2,5,6,7 to insert items on places 3,4
UPDATE t1 SET order_in_list = (order_in_list + $child_no)
WHERE order_in_list > $record->order_in_list
// Okay, set IDs for direct children
foreach( $children as $child){
UPDATE t1 SET order_in_list = $root_order, depth_in_list = $record->depth_in_list+1
WHERE id = $child->id
$root_order++;
}
}
COMMIT
This way you'll get records like:
First category, 1, 1
Second category 3, 1
Sub category, 2, 2
Which you could display with simple loop:
$last_depth = 0;
foreach( (SELECT * FROM t1 ORDER by `order_in_list`) as $row){
if( $last_detph > $row['depth_in_list'])){
// Close level </ul>
} else if($last_detph < $row['depth_in_list']){
// Opening level <ul>
} else {
// The same depth
}
$last_depth = $row['depth_in_list'];
}
Without modifying database
It would be probably most effective to build two arrays containing root elements and all elements:
$root_elements = array();
$all_elements = array();
foreach( (SELECT * FROM t1) as $row){
// Store details into all_elements, note that entry may have already be created when
// processing child node
if( isset( $all_elements[$row['id']])){
// set details
} else {
$all_elements[$row['id']] = $row;
$all_elements[$row['id']]['children'] = array(); // Array of child elements
}
if( $row['parent_id'] == NULL){
$all_elements[] = $row['id']; // Add row element
} else {
if( isset( $all_elements[ $row[ 'parent_id']])){
$all_elements[ $row[ 'parent_id']]['children'][] = $row['id'];
} else {
// Create new record:
$all_elements[ $row[ 'parent_id']] = array();
$all_elements[ $row[ 'parent_id']]['children'] = array($row['id']);
}
}
}
And then write it as:
foreach( $root_elements as $element_id){
write_recursive( $all_elements[ $element_id]);
}
// And display
function write_recursive( $element)
{
echo '<ul>...';
if( count( $element['children'])){
foreach( $element['children'] as $child){
write_recursive( $all_elements[ $child]);
}
}
echo '</ul>';
}
You better create class for that (to replace using global variables), but you should have a solid way to do this. Anyway try avoid using this with large number of records (I wouldn't go past 2000-5000 menu entries), try to at least cache it.
Note: solutions are oriented towards minimal number of requests on database when displaying list.

Answer 2

you can use complicated query or something like this
foreach ($catsid as $catid) {
...
$subquery_cat = "SELECT * FROM ^categories WHERE parentid='".$catid['categoryid']."'";
$query = qa_db_query_sub($subquery_cat);
$subcatsid = qa_db_read_all_assoc($query);
// wrap into html
...
}