Dynamically load data into bootstrap accordion navigation bar

Question

I have made a bootstrap accordion navigation bar that loads data dynamically from a database with PHP.

Here are the two tables that I use:

CREATE TABLE IF NOT EXISTS `top_tier` (
  `id` varchar(50) NOT NULL,
  `name` varchar(255) NOT NULL,
  `date_created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `created_by` varchar(50) NOT NULL,
  `date_edited` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `status` int(11) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
)

CREATE TABLE IF NOT EXISTS `sub_tier` (
  `id` varchar(50) NOT NULL,
  `name` varchar(255) NOT NULL,
  `type` varchar(50) NOT NULL,
  `date_created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `created_by` varchar(50) NOT NULL,
  `date_edited` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `edited_by` varchar(50) NOT NULL,
  `parent_id` varchar(50) NOT NULL,
  `status` int(11) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
)

Basically the table top_tier has the main items of the accordion navigation bar. An entry in the top_tier table can have multiple children from the table sub_tier and that said entry from the sub_tier table can have children too from the column parent_id. When I click an item from the accordion that's from the top_tier table, it shows its children. Then if I click an item from the top_tier item, it shows its children items if it has any.

Here is the code for the accordion:

    <div id="MainMenu">
  <div class="list-group panel">
    <?php
    $top_items =  $obj->getTopTierItems();
    foreach($top_items as $top_item) {
    extract($top_item);
    ?>

    <a href="#<?php echo $id;?>" class="strong list-group-item" data-toggle="collapse" data-parent="#MainMenu">
      <?php echo $name;?> 
      <i class="fa fa-caret-down"></i>
    </a>

    <div class="output collapse" id="<?php echo $id; ?>">
      <?php 
      $sub_items = $obj->getSubTierItems($id); 
      foreach($sub_items as $sub_item) {
        $id2 = $sub_item['id'];
        $name2 = $sub_item['name'];
        $parent_id = $sub_item['parent_id'];
      ?>
        <a href="#<?php echo $id2?>" class="strong list-group-item" data-parent="#<?php echo $parent_id; ?>">
          <?php echo $name2;?>
        </a>

        <div class="output collapse" id="<?php echo $id2; ?>">

        </div>
        <?php
        }
        ?>
    </div>

    <?php 
    }
    ?>
  </div>
</div>

Here is the PHP that fetches the data from the top_tier table:

public function getTopTierItems(){

        $SQL = "
            SELECT

            id,
            name

            FROM 
                top_tier
            WHERE
                status = 1  
        ";              
        $results = $this->db_query_listx($SQL);
        return $results;
    }

Here is the PHP that fetches the data from the sub_tier table:

public function getSubTierItems($id){

        $SQL = "
            SELECT

            id,
            name,
            parent_id

            FROM
                sub_tier
            WHERE
                status = 1
            AND
                parent_id='$id'

        ";              
        $results = $this->db_query_listx($SQL);
        return $results;
    }

Here is the function that controls the data from the database:

public function db_query_listx($SQL){
        global $connect;
        if ($resultset = $connect->query($SQL)) {
            if ($resultset->num_rows > 0) {

                $data = array();
                    while( $row = $resultset->fetch_assoc() ) {
                        $data[] = array_change_key_case($row);
                    }
                }else {
                $data = NULL;
            }
        } else {
            $data = die("<CENTER><DIV class='error'>ERROR: " . $connect->error . "<BR> ( $SQL ) <HR>
                             Please report this to <a href='#'>webmaster</a>.</DIV></CENTER>");
        }
        $resultset->close();
        return $data;
    }

Answer 1

Timestamp

Why do you insert an invalid value '0000-00-00 00:00:00' into your TIMESTAMP columns by DEFAULT? I think you would be much better served by using something relevant, like CURRENT_TIMESTAMP...

  `date_created` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,

And...

  `date_edited` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,

Identifiers

Is there any particular reason your identifiers are varchar? Seems odd. Example:

  `id` varchar(50) NOT NULL,

To me should be:

  `id` INT NOT NULL AUTO_INCREMENT,

PDO

This function could use a MySQL procedure (and PHP PDO):

public function getTopTierItems(){

And this one especially:

public function getSubTierItems($id){

Answer 2

Your database structure needs work.

1. id columns should almost always be INTs, not VARCHARs. That's just silly design. Similarly, parent_id should be an INT.
2. created_by should be foreign keyed to some users table.
3. status is not necessarily a good name. If you only need to differentiate between active and inactive, use a TINYINT and name it something like isActive. If you need more states, then assign a value like 'active' or 'inactive' or 'draft', instead of 1 and 0.
4. There's no reason to have a separate table for top_tier and sub_tier. Rename sub_tier to something else (nav_items?) and get rid of top_tier. Whenever you have a top-tier item, set its parent_id to 0 or NULL.