wpdb COALESCE won’t work

I am struggling to get the result using COALESCE from custom table. I need to run a second query if the first results null but wpdb resulting query string itself rather than the result.

$query = "SELECT coalesce(";
$query .= "(SELECT order_number FROM wp_gs_p_cart ";
$query .= "WHERE group_user = %d AND group_id = %d AND identifier = %s ORDER BY id DESC LIMIT 1),";
$query .= "(SELECT order_number FROM wp_gs_p_cart ORDER BY id DESC LIMIT 1)";
$query .= ");";

$prepare = $wpdb->prepare($query, $user_id, $group_id, $identifier);

return $wpdb->get_results($prepare);

// or 

return $wpdb->get_row($prepare);

Result

Array
(
    [0] => stdClass Object
        (
            [coalesce((SELECT order_number FROM wp_gs_p_cart WHERE group_user = 73 AND group_id = 298 AND identifier = 'AtR4deAVgU4Ensi1_1ac2b33a4df7c5f0cf148d6232074352' ORDER BY id DESC LIMIT 1),(SELECT order_number FROM wp_gs_p_cart ORDER BY id DESC LIMIT 1))] => 3333
        )

)