In witch table are orders ?

I would fetch the orders using functions in preference to accessing the orders table directly, so in outline:

$user_id = get_current_user_id();
$posts = get_posts( array(
    'numberposts' => -1,
    'meta_key'    => '_customer_user',
    'meta_value'  => $user_id,
    'post_type'   => wc_get_order_types( 'view-orders' ),
    'post_status' => array( 'wc-pending',  'wc-on-hold', 'wc-processing' ),
) );
foreach( $posts as $post ) {
  $order = new WC_Order( $post->ID );
  // etc