How to sum all data from a table

Question

I have the 'orders' table where all the orders that were made are, I would just add all the orders and show on the screen.

In the example above I have 8 orders, on the screen will simply have "Number of orders made 8", if you understood.

    <?php 
        require  'conexao_pedidos.php';
        $sql = query("SELECT order_id FROM orders GROUP BY order_id;");
        $result=$conn->query($sql);
        while($row=$result->fetch_assoc()){
    ?>
    <div class="text-center"><?=  $row ?></div>
    <?php
		}
		?>

Answer 1

To count the number of records from a table you have two options, or by SQL using the aggregate function COUNT(*) that returns the count of the number of rows recovered in a query or by PHP through property num_row of the object mysqli_result(I believe to be mysqli because PDO does not have the method fetch_assoc()).

By SQL using COUNT(*):

$sql = query("SELECT COUNT(*) as pedidos FROM orders;"); //Aqui eu não entendi o uso do GROUP BY order_id pois order_id parece ser a chave primária da tabela
$row= $conn->query($sql)->fetch_assoc(); // A consulta irá retornar apenas uma linha
echo "Número de pedidos: ".$row['pedidos'];

By PHP using mysqli_result::num_rows:

$sql = query("SELECT order_id FROM orders;");
$result= $conn->query($sql);
echo "Número de pedidos: ".$result->num_rows;