Two Data Base Design Comparison

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SQL-Server

SQL-Server-2008

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I have Two Data base Design approach , I develop a system (it is an accounting system )
during my data base design i found that , i have Purchase Order Table , Purchase Bill Table and Purchase Return Table , Of course Each Order , Purchase , Or Return Must Have it is Own Item , Suppose that Each item information For the three Bills Is the Same , So for now i have A new Table Called Bill Items , the wright Way , is to make One Table For all items of the three bill and it will be as follow
BillItems table (F1 , F2 , F3 ..... ,
PurchaseOrderID(Allow Null),PurchaseBillID (Allow Null),PurchaseReturnID(Allow Null))

this is the First Solution,

the Second Solution is to make the BillItem Table Divide it into three tables
1 - PurchaseOrderItems (F1 , F2 , F3 , .... PurchaseOrderID(does not allow null))
2 - PurchaseBillItems (F1 , F2 , F3 , .... PurchaseBillID(does not allow null))
1 - PurchaseReturnItems (F1 , F2 , F3 , .... PurchaseReturnID(does not allow null))


now i want to know which of the Solutions is the best...?
thanks Every One.