Discount in Pricing Rule for All Item Group

I cant use the discount in pricing rule and apply to all item groups because in the doctype of pricing rule the item code is mandatory and if i moved the mandatory for the item code in the sales order when i choose the item code non of the items can be shown in this sales order can anyone help

Could not understand the issue quite clearly. Can you please elaborate a little bit more with some screenshots?

You might set “Item Code” field mandatory from Customize Form -> Pricing Rule. Please check and confirm.