Magento 2 How to Add a New Column to Orders Grid

After lots of digging into Magento's core code, I found a solution to my question. Instead of adding a column to the grid via the database, I created a UI component sales_order_grid.xml under [COMPANY]/[MODULE]/view/adminhtml/ui_component/sales_order_grid.xml

<?xml version="1.0" encoding="UTF-8"?>
<listing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <columns name="sales_order_columns">
        <column name="export_status" class="[COMPANY]\[MODULE]\Ui\Component\Listing\Column\Status">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="visible" xsi:type="boolean">true</item>
                    <item name="label" xsi:type="string" translate="true">XML Exported</item>
                </item>
            </argument>
        </column>
    </columns>
</listing>

Then created the UI class under [COMPANY]/[MODULE]/Ui/Component/Listing/Column/Status.php

namespace [COMPANY]\[MODULE]\Ui\Component\Listing\Column;

use \Magento\Sales\Api\OrderRepositoryInterface;
use \Magento\Framework\View\Element\UiComponent\ContextInterface;
use \Magento\Framework\View\Element\UiComponentFactory;
use \Magento\Ui\Component\Listing\Columns\Column;
use \Magento\Framework\Api\SearchCriteriaBuilder;

class Status extends Column
{
    protected $_orderRepository;
    protected $_searchCriteria;

    public function __construct(ContextInterface $context, UiComponentFactory $uiComponentFactory, OrderRepositoryInterface $orderRepository, SearchCriteriaBuilder $criteria, array $components = [], array $data = [])
    {
        $this->_orderRepository = $orderRepository;
        $this->_searchCriteria  = $criteria;
        parent::__construct($context, $uiComponentFactory, $components, $data);
    }

    public function prepareDataSource(array $dataSource)
    {
        if (isset($dataSource['data']['items'])) {
            foreach ($dataSource['data']['items'] as & $item) {

                $order  = $this->_orderRepository->get($item["entity_id"]);
                $status = $order->getData("export_status");

                switch ($status) {
                    case "0":
                        $export_status = "No";
                        break;
                    case "1";
                        $export_status = "Yes";
                        break;
                    default:
                        $export_status = "Failed";
                        break;

                }

                // $this->getData('name') returns the name of the column so in this case it would return export_status
                $item[$this->getData('name')] = $export_status;
            }
        }

        return $dataSource;
    }
}

My solution may be a bit more efficient since it follows the native way of adding a column to the grid, and you won't have to load every order displayed on the page to obtain the column data (utilizing the sales_order_grid table instead). The above is a great example of how to create a customized renderer though.

vendor/[vendor]/[package]/view/adminhtml/ui_component/sales_order_grid.xml

<!-- Add the column "my_column" (My Column) to the sales order grid. -->
<listing xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
<columns name="sales_order_columns">
    <column name="my_column">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="filter" xsi:type="string">text</item>
                <item name="label" xsi:type="string" translate="true">My Column</item>
            </item>
        </argument>
    </column>
</columns>

Please note that you must enable the column using the drop-down widget above the order grid before it appears.

vendor/[vendor]/[package]/etc/di.xml

<!-- Sync the column "my_column" between the sales_order and sales_order_grid tables -->
<virtualType name="Magento\Sales\Model\ResourceModel\Order\Grid" type="Magento\Sales\Model\ResourceModel\Grid">
    <arguments>
        <argument name="columns">
            <item name="my_column" xsi:type="string">sales_order.my_column</item>
        </argument>
    </arguments>
</virtualType>

Sample setup code to add a column to sales_order_grid table (use this in your install/upgrade script). The same code works for the sales_order table by the way.

$setup->getConnection()->addColumn(
        $setup->getTable('sales_order_grid'),
        'my_column',
        [
            'type' => \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
            'length' => 255,
            'nullable' => true,
            'comment' => 'My Column'
        ]
    );

Hope it helps! :-)