移动加权平均成本计算方法,谢谢大家

表proitem 
id pro_id(产品ID)  pro_amount(数量)  pro_price(单价)  pro_unitcost(成本单价)                      pro_money(金额) 
1    1              5                  10    
1    1              10                  8  
1    1              5                    6    
1    1              10                  5    
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如何得到 
id pro_id(产品ID)  pro_amount(数量)  pro_price(单价)pro_unitcost(成本单价)                          pro_money(金额) 
1    1              5                  10      10                                            50 
1    1              10                  8    (5*10+10*8)/(5+10)=8.667                        10*8.667=86.67 
1    1              5                    6    (5*10+10*8.67+5*6)/(5+10+5)=8.335              5*8.335=41.675 
1    1              10                  5    (5*10+10*8.67+5*8.335+10*5)/(5+10+5+10)=5.944  10*5.944=59.44 
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谢谢大家