计算产品库存的加权平均成本 [英] Calculating the Weighted Average Cost of products stock
问题描述
我必须计算产品的库存成本，因此对于每次购买后的每种产品，我必须重新计算 加权平均成本 。
I have to calculate my products stock cost, so for every product after each buy, i have to recalculate the Weighted Average Cost.
我认为每次进出后，都会带给我当前产品的库存：
I got a view thats bring me the current product's stock after each in/out:
document_type document_date product_id qty_out qty_in price row_num stock_balance
SI 01/01/2014 52 0 600 1037.28 1 600
SI 01/01/2014 53 0 300 1357.38 2 300
LC 03/02/2014 53 100 0 1354.16 3 200
LC 03/02/2014 53 150 0 1355.25 4 50
LC 03/02/2014 52 100 0 1035.26 5 500
LC 03/02/2014 52 200 0 1035.04 6 300
LF 03/02/2014 53 0 1040 1356.44 7 1090
LF 03/02/2014 52 0 1560 1045 8 1860
LC 04/02/2014 52 120 0 1039.08 9 1740
LC 04/02/2014 53 100 0 1358.95 10 990
LF 04/02/2014 52 0 600 1038.71 11 2340
LF 04/02/2014 53 0 1040 1363.3 12 2030
LC 05/02/2014 52 100 0 1037.78 13 2240
LF 15/03/2014 53 0 20 1365.87 14 2050
LF 15/03/2014 52 0 50 1054.19 15 2290
我想添加一个计算得出的 WAC 字段，如下所示：
I want to add a calculated WAC field as above:
document_type document_date product_id qty_out qty_in price row_num stock_balance WAC
SI 01/01/2014 52 0 600 1 037,28 1 600 1037,28000000000
SI 01/01/2014 53 0 300 1 357,38 2 300 1357,38000000000
LC 03/02/2014 53 100 0 1 354,16 3 200 1357,38000000000
LC 03/02/2014 53 150 0 1 355,25 4 50 1357,38000000000
LC 03/02/2014 52 100 0 1 035,26 5 500 1037,28000000000
LC 03/02/2014 52 200 0 1 035,04 6 300 1037,28000000000
LF 03/02/2014 53 0 1040 1 356,44 7 1090 1356,48311926606 --((1357,38*50)+(1040*1356,44))/(1090)
LF 03/02/2014 52 0 1560 1 045,00 8 1860 1043,75483870968 --((1037,28*300)+(1560*1045))/(1860)
LC 04/02/2014 52 120 0 1 039,08 9 1740 1043,75483870968
LC 04/02/2014 53 100 0 1 358,95 10 990 1356,48311926606
LF 04/02/2014 52 0 600 1 038,71 11 2340 1042,46129032258 --((1043,75483870968*1740)+(600*1038,71))/(2340)
LF 04/02/2014 53 0 1040 1 363,30 12 2030 1359,97000000000 --((1356,48311926606*990)+(1040*1363,3))/(2030)
LC 05/02/2014 52 100 0 1 037,78 13 2240 1042,46129032258
LF 15/03/2014 53 0 20 1 365,87 14 2050 1360,03301857239 --((1359,97551136621*2030)+(20*1365,87))/2050
LF 15/03/2014 52 0 50 1 054,19 15 2290 1042.71737568672 --((1042.46129032258*2240)+(50*1054.19))/2290
只有一种文档类型每个产品的'SI'（初始库存），与之相关的价格为初始WAC 。
There is only one and just one document type 'SI' (initial stock) for each product, and the price associated with it is the initial WAC.
这里是 SQL Fiddle 示例。
如果有人可以提供帮助，我将无法解决。
If someone can help with this, i can't figure it out.
编辑：我只是通过在小数点后显示9个数字来提高精度来更新计算的数字。
Edit: I've juste updated the calculated numbers by increasing precision by displaying 9 numbers after the decimal point.
推荐答案
您需要使用递归CTE：
You need to use recursive CTE:
with recursive
stock_temp as (
select
*,
row_number() over(partition by product_id order by row_num) as rn
from
stock_table
)
,cte as (
select
document_type, document_date,
product_id, qty_out, qty_in, price,
row_num, stock_balance, rn,
price as wac
from
stock_temp where document_type = 'SI'
union all
select
sub.document_type, sub.document_date,
sub.product_id, sub.qty_out, sub.qty_in, sub.price,
sub.row_num, sub.stock_balance, sub.rn,
case when sub.qty_in = 0 then main.wac else
((sub.stock_balance - sub.qty_in) * main.wac + sub.qty_in * sub.price)
/ ((sub.stock_balance - sub.qty_in) + sub.qty_in) end as wac
from
cte as main
join stock_temp as sub
on (main.product_id = sub.product_id and main.rn + 1 = sub.rn)
)
select * from cte
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