Add a column to the PMPro orders table that shows the original subscription order.

my_original_sub_order_col.php

<?php
/**
 * Add a column to the PMPro orders table that shows the original subscription order.
 * Requires PMPro 2.5+
 * Add this code to a Code Snippet or custom plugin.
 */
function my_original_sub_order_col_header($order_ids) {
	?>
    <th>Original Order</th>
    <?php
}
add_action('pmpro_orders_extra_cols_header', 'my_original_sub_order_col_header');

function my_original_sub_order_col_body($order) {
    ?>

    <td>
	<?php 
		if ( method_exists( 'MemberOrder', 'get_original_subscription_order' ) ) {
			$original_order = $order->get_original_subscription_order();
			if ( ! empty( $original_order ) ) {
			?>
			<a href="<?php echo esc_url( admin_url( 'admin.php?page=pmpro-orders&order=' . $original_order->id ) ); ?>"><?php echo $original_order->code;?></a>
			<?php
			} else {
				echo "N/A";
			}
		} else {
			echo "N/A";
		}
	?>
	</td>

    <?php
}
add_action('pmpro_orders_extra_cols_body', 'my_original_sub_order_col_body');