Categories_model::getCategories PHP Method

    public function getCategories($parent = NULL)
    {
        $sql = "SELECT cat1.category_id, cat1.name, cat1.description, cat1.image, ";
        $sql .= "cat1.priority, cat1.status, child.category_id as child_id, sibling.category_id as sibling_id ";
        $sql .= "FROM {$this->db->dbprefix('categories')} AS cat1 ";
        $sql .= "LEFT JOIN {$this->db->dbprefix('categories')} AS child ON child.parent_id = cat1.category_id ";
        $sql .= "LEFT JOIN {$this->db->dbprefix('categories')} AS sibling ON sibling.parent_id = child.category_id ";
        if ($parent === NULL) {
            $sql .= "WHERE cat1.parent_id >= 0 ";
        } else {
            if (empty($parent)) {
                $sql .= "WHERE cat1.parent_id = 0 ";
            } else {
                $sql .= "WHERE cat1.parent_id = ? ";
            }
        }
        if (APPDIR === MAINDIR) {
            $sql .= "AND cat1.status = 1 ";
        }
        $query = $this->db->query($sql, $parent);
        $result = array();
        if ($query->num_rows() > 0) {
            foreach ($query->result_array() as $row) {
                $result[$row['category_id']] = $row;
            }
        }
        return $result;
    }