add-column-to-order-list.php

<?php

add_filter( 'manage_edit-shop_order_columns', 'toret_barcode_column', 99999 );
function barcode_column($columns) {
    	$new_columns = array();
    	foreach($columns as $key => $item){
      		$new_columns[$key] = $item;
      		if($key == 'cb'){
         		$new_columns['barcode'] = __( 'Barcode', 'woocommerce' );
      		}
    	}    
    	return $new_columns;
  	}

add_action( 'manage_shop_order_posts_custom_column', 'toret_barcode_column_display', 10, 2 );
function barcode_column_display($column_name, $post_id){
    	global $post;

      	if ( $column_name == 'barcode' ) { 
        	//$field = get_post_meta( $post_id, 'barcode', true );
        	echo 'barcode';
      	}      	

  	}