Magento 2 – Are entity_id and order_id the Same?

I think we should map some more tables:

Magento 1                     || Magento 2
sales_flat_order                 sales_order
sales_flat_order_address         sales_order_address
sales_flat_order_grid            sales_order_grid
sales_flat_order_item            sales_order_item
sales_flat_order_payment         sales_order_payment
sales_flat_order_status_history  sales_order_status_history

If we had the invoices and shipments, we need to map more tables.

Note: when we want to clear the order from Magento 2, we can use this module.

If you can load your CSV file content then This is the way to import Bulk URL Rewrite:

Add below Code into script than run it.

// MAGENTO START
    include('../../../app/bootstrap.php');

    use Magento\Framework\App\Bootstrap;
    use Magento\Framework\App\Config\ScopeConfigInterface;
    use Magento\Store\Model\StoreManagerInterface;
    use Magento\Framework\Exception\LocalizedException;
    use Magento\UrlRewrite\Model\UrlFinderInterface;
    use Magento\UrlRewrite\Service\V1\Data\UrlRewrite;

    $bootstrap = Bootstrap::create(BP, $_SERVER);
    $objectManager = $bootstrap->getObjectManager();

    $state = $objectManager->get('Magento\Framework\App\State');
    $state->setAreaCode('frontend');

    $scopeConfig = $objectManager->create('Magento\Framework\App\Config\ScopeConfigInterface');

    $_storeManager = $objectManager->create('Magento\Store\Model\StoreManagerInterface');
    $dataProcessor = $objectManager->create('Magento\Framework\Reflection\DataObjectProcessor');

    $storeId = $_storeManager->getDefaultStoreView()->getStoreId();    

foreach($data as $key => $rec)
{   
    $urlRewrite = $objectManager->create(\Magento\UrlRewrite\Model\UrlRewrite::class);

    $urlRewrite->load(0);

    $model = $urlRewrite;
    $product['entity_type']      = $rec['entity_type'];
    $product['request_path']     = $rec['request_path'];
    $product['target_path']      = $rec['target_path'];
    $product['redirect_type']    = $rec['redirect_type'];
    $product['store_id']         = $rec['store_id'];

    $objectManager->get(\Magento\UrlRewrite\Helper\UrlRewrite::class)->validateRequestPath($product['request_path']);
    $model->setEntityType($product['entity_type'])
        ->setRequestPath($product['request_path'])
        ->setTargetPath($product['target_path'])
        ->setRedirectType($product['redirect_type'])
        ->setStoreId($product['store_id'])
        ->setDescription("Imported Urls");

    $model->save();
}

echo "Successfully Imported!";

$data is the data from your csv or file. which should have same name column as above imported.

entity_id is not required is you choose entity_type "custom"

Set appropriate path to include bootstrap for "include('../../../app/bootstrap.php');", I have added my script in "pub/script/vendor", So I have applied path like this.