PHP - Show A Category Using An Array

$result = mysql_query("SELECT * FROM user_table WHERE hash='$session_id'");
$rowuser = mysql_fetch_array($result);

$result = mysql_query("SELECT * FROM products");
$rowproducts = mysql_fetch_array($result);

<?php
// Establish SQL Connection.

$mysqli			=	mysqli_connect( $sql['host'], $sql['user'], $sql['pass'], $sql['db'] ) or die( "DARN");
$query			=	$mysqli->query( "SELECT * FROM folders ORDER BY name ASC" );
$num_rows	=	$query->num_rows;


echo "Found <b>" . $num_rows . "</b> row(s) in the database!<br>";


	while ( $row = mysqli_fetch_array( $query ) )
	{
		// DO NOT REMOVE
		$id		=	$row['id'];
		$name	=	$row['name'];
		$parent	=	$row['parent'];
		
		/***************************************************************************************************/
		
		if ( $parent == 0 )
		{
			echo $id . " " . $name . " " . $parent . "<br>";
			
			$query2	=	$mysqli->query( "SELECT * FROM folders WHERE parent = " . $id . " ORDER BY name ASC" );
			
			while ( $row2 = mysqli_fetch_array( $query2 ) )
			{
				echo "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" . $row2['name'] . "<br>";
			}
		}
	}
?>

An array of "categories" is given:

    $categories = array(
        array("id" => 1, "title" => "Pants", "children" => array(
            array("id" => 2,
                "title" => "Boots",
                "children" => array(
                    array("id" => 3, "title" => "Leather"),
                    array("id" => 4, "title" => "Textile"),
                ),
            ),
            array("id" => 5, "title" => "Sneakers"),
        ),
        ),
        array(
            "id" => 6,
            "title" => "Sort",
            "children" => array(
                array(
                    "id" => 7,
                    "title" => "Balls",
                ),
            ),
        ),
    );

I need to write a function searchCategory ($categories, $id) that returns the name of the category by the category ID.

Help me please.

I need some help with the category part on a old project .

The problem what I have at this moment that, when I click on the category all categories are showing up on the category.php page itself.

What whI wanne have when I click Uncategorised that in the category.php page only post are showing that have been made in Uncategorised category

function get_posts() {
    $sql = "SELECT 
              `blog`.`post_id` AS `id`,
              `blog`.`post_title` AS `title`,
              LEFT(`blog`.`post_body`, 512) AS `preview`,
              `blog`.`post_user` AS `user`,
              `blog_categories`.`id` AS `category_id`,
              `blog_categories`.`name` AS `category_name`,
              DATE_FORMAT(`blog`.`post_date`,  '%d-%m-%Y %H:%i') AS `date`,
              `blog_comments`.`total_comments`,           
              DATE_FORMAT(`blog_comments`.`last_comment`, '%d-%m-%Y %H:%i') AS `last_comment`
            FROM `blog`
               INNER JOIN `blog_categories` ON `blog_categories`.`id` = `blog`.`cat_id`
            LEFT JOIN ( 
                SELECT 
                   `post_id`,
                   COUNT(`comment_id`) AS `total_comments`,
                   MAX(`comment_date`) AS `last_comment`
                FROM `blog_comments`
                GROUP BY `post_id`
              ) AS `blog_comments`
              ON `blog`.`post_id` = `blog_comments`.`post_id`
              ORDER BY `blog`.`post_date` DESC";

    $posts = mysql_query($sql);

    $rows = array();
    while (($row = mysql_fetch_assoc($posts)) !== false) {
        $rows[]= array(
            'id'             => $row['id'],
            'title'          => $row['title'],
            'preview'        => $row['preview'],
            'user'           => $row['user'],   
            'date'           => $row['date'],           
            'category_id'    => $row['category_id'],    
            'category_name'  => $row['category_name'],
            'total_comments' => ($row['total_comments'] === null) ? 0 : $row['total_comments'],
            'last_comments'  => ($row['last_comment'] === null) ? 'never' : $row['last_comment']                                                            
        );
    }
    
    return $rows;
}

function get_post($pid) {
    $pid = (int)$pid;

    $sql =   "SELECT
                `post_title` AS `title`,
                `post_body` AS `body`,
                `post_user` AS `user`,
                `blog_categories`.`id` AS `category_id`,
                `blog_categories`.`name` AS `category_name`,
                DATE_FORMAT(`post_date`, '%d-%m-%Y %H:%i') AS `date`
            FROM `blog` 
                INNER JOIN `blog_categories` ON `blog_categories`.`id` = `blog`.`cat_id`
            WHERE `post_id` = '$pid'";

    $post = mysql_query($sql);
    $post = mysql_fetch_assoc($post);

    $post['blog_comments'] = get_comments($pid);

    return $post;      
}

The old way was like this 

   if ( isset($cat_id)) {
      $cat_id = (int) $cat_id;
      $query .= " WHERE `blog_categories`.`id` = $cat_id";
   }  

Database 

blog_categories

id | name |

----------- 

4 Uncategorised

1 Youtube

blog 

post_id | cat_id | post_title | post_body | post_user | post_date 

-----------------------------------------------------------------------------------

4 | 1 | Youtube | Youtube link | Admin | 2020-09-13 16:10:53

Web server
Apache/2.2.21 (Win64) PHP/5.3.10
MySQL-client versie: mysqlnd 5.0.8-dev - 20102224 - $Revision: 321634 $
PHP uitbreiding: mysqli Documentatie

phpMyAdmin
Versie informatie: 3.4.10.1, meest recente versie: 5.0.2

I hope someone can help me with this problem