Include discount amount on subtotal in order export file Magento 2.2.2

Question

I would like to export sales order from sales->Orders and the column subtotal(in csv and excel file) which should include the discount amount which we have apply while purchasing the product.

for example i have subtotal as 133 in my current exported order file for this order i have aplayed a coupon which will reduce 20$ from the total amount so i have to show in subtotal as 133-20=113 in subtotal field it should show 113 instead of 133

Note:it should show only in exported file