Membuat dropdown selected sesuai dengan database

ane penginnya buat dropdown yang retrive data dari database, dan selected di nilai yang ditentukan.

Ane udah coba utak-atik tapi keliatannya otak ane udah mentok,

<select name="dropdown_cat_id_title" id="">

            <?php
                $qry = "SELECT * FROM categories";
                $select_categories_id = mysqli_query($connec_db, $qry);

                while ($row = mysqli_fetch_assoc($select_categories_id))
                    {
                        $cat_id__php = $row ['cat_id'];
                        $cat_title__php = $row ['cat_title'];

                        if ($post__category_id_php  == $cat_id__php)
                        {
                            $select_value_dropdown = "selected";
                        }
                        $select_final = $select_value_dropdown;

                        echo"<option value='{$cat_id__php}' $select_final >{$cat_title__php}</option>";
                    }
            ?>

\</select>