I have to calculate my products stock cost, so for every product after each buy, i have to recalculate the Weighted Average Cost.
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
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
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.
Here is a SQL Fiddle sample.
If someone can help with this, i can't figure it out.
Edit: I've juste updated the calculated numbers by increasing precision by displaying 9 numbers after the decimal point.
You need to use recursive CTE:
SQLFiddle
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
I have spent several hours on this moving average! Mainly because of the not reliable window function first/last/nth_value, according to Postgresql documentation on window functions:
This is likely to give unhelpful results for nth_value and particularly last_value.
The answer is incomplete. Things to do:
- make WAC stay the same value when qty_in = 0 (now it is zeroed out)
- WAC is not calculated based on previous WAC but on "previous" price, that's why there are increasing differences between WAC calculated by me and presented by You
SQLFiddle
Here what i did using function:
CREATE TYPE stock_table_with_wac AS
(document_type character varying,
document_date date,
product_id bigint,
qty_out double precision,
qty_in double precision,
price double precision,
row_num bigint,
stock_balance double precision,
wac double precision);
CREATE OR REPLACE FUNCTION calculate_wac_value()
RETURNS SETOF stock_table_with_wac AS
$BODY$
DECLARE
r_article stock_table_with_wac%rowtype;--maintain the liste of all products with there wac's value
r_in_out_article stock_table_with_wac%rowtype;--Each other records
BEGIN
--For each products
FOR r_article IN SELECT *, price FROM stock_table where document_type='SI' order by row_num
LOOP
return next r_article;
FOR r_in_out_article IN SELECT * FROM stock_table where document_type<>'SI' and product_id=r_article.product_id order by row_num
LOOP
--If there is an entry calculate the wac
if r_in_out_article.qty_in >0 then
r_in_out_article.wac:=((r_article.price * (r_in_out_article.stock_balance - r_in_out_article.qty_in)) + (r_in_out_article.qty_in * r_in_out_article.price))/(r_in_out_article.stock_balance);
--Update the wac value of the product
r_article.price:= r_in_out_article.wac;
else --The waca value still inchanged:
r_in_out_article.wac:= r_article.price;
end if;
RETURN NEXT r_in_out_article; -- return current row with caluculated wac if any
END LOOP;
return next r_article;
END LOOP;
RETURN;
END
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100
ROWS 1000;
ALTER FUNCTION calculate_wac_value()
OWNER TO postgres;
select * from calculate_wac_value();
It seems to have a correct output. Is it a good idea to process like this?
There already is a aggregate function in C for PostgreSQL available, and it will probably calculate much faster than any solution in SQL:
https://github.com/Kozea/weighted_mean
I have used the data provided in the following article which was meant for FIFO logic.
https://www.red-gate.com/simple-talk/sql/performance/set-based-speed-phreakery-the-fifo-stock-inventory-sql-problem/
Here, the returns are considered, but I take them at average price.
Here is the table structure:
ID ArticleID TranDate TranCode Items Price WACPrice WACRunningTotal
1 11782 2009-01-01 00:00:41.000 IN 809 256.82 256.82 NULL
2 16967 2009-01-01 00:00:50.000 IN 372 134.44 134.44 NULL
3 13078 2009-01-01 00:01:21.000 IN 532 201.69 201.69 NULL
4 10918 2009-01-01 00:01:34.000 IN 717 348.79 348.79 NULL
5 18871 2009-01-01 00:01:34.000 IN 1045 88.25 88.25 NULL
6 22379 2009-01-01 00:03:01.000 IN 401 326.59 326.59 NULL
7 24049 2009-01-01 00:03:24.000 IN 222 54.54 54.54 NULL
8 12570 2009-01-01 00:03:33.000 IN 731 29.25 29.25 NULL
9 10327 2009-01-01 00:03:33.000 IN 407 222.69 222.69 NULL
10 21548 2009-01-01 00:03:49.000 IN 400 254.05 254.05 NULL
11 15155 2009-01-01 00:03:51.000 IN 719 320.02 320.02 NULL
12 22706 2009-01-01 00:04:00.000 IN 331 25.91 25.91 NULL
13 19126 2009-01-01 00:04:16.000 IN 289 305.47 305.47 NULL
14 21722 2009-01-01 00:04:39.000 IN 434 3.80 3.80 NULL
15 20811 2009-01-01 00:05:57.000 IN 1043 316.57 316.57 NULL
16 21998 2009-01-01 00:06:01.000 IN 1009 15.18 15.18 NULL
17 12928 2009-01-01 00:06:45.000 IN 1122 265.71 265.71 NULL
18 14150 2009-01-01 00:07:36.000 IN 730 148.91 148.91 NULL
19 22307 2009-01-01 00:08:09.000 IN 986 184.38 184.38 NULL
20 17472 2009-01-01 00:08:34.000 IN 1182 62.73 62.73 NULL
please follow the ddl statement in the above mentioned post.
I have use Cte, but for 1000001 records, it maxes out the maxrecursion count.
So I created a procedure to execute by one item id which can be iterated by another procedure.
I have added two columns to the stock table, WACPrice and WACRunningTotal.
please find my code below:
alter proc sp_GetInventoryDetails_ByWAC
-- sp_GetInventoryDetails_ByWAC 10017
@ArticleId int
as
begin
-- select * from #stocktemp order by trandate
--select *, 0 as WACRunningTotal into #StockTemp from stock where articleid=10000 order by TranDate;
;WITH y AS
(
SELECT articleid,TranDate,trancode, items, rn = ROW_NUMBER() OVER (ORDER BY TranDate)
FROM stock where ArticleID =@ArticleId
), x AS
(
SELECT articleid, TranDate,trancode, rn, items, rt = items
FROM y
WHERE rn = 1
UNION ALL
SELECT y.articleid,y.TranDate,y.trancode, y.rn, y.items,case when y.TranCode='OUT' then x.rt - y.items else x.rt+y.Items end
FROM x INNER JOIN y
ON y.rn = x.rn + 1
)
update st set st.WACRunningTotal=x.rt
from stock st
inner join x on x.ArticleID=st.ArticleID and x.TranDate=st.TranDate and x.TranCode=st.TranCode and isnull(st.WACRunningTotal,0)=0
OPTION (MAXRECURSION 0);
;WITH StockCTE
AS (SELECT articleid,
items,
WACRunningTotal,
WACPrice,
trandate,
ROW_NUMBER() OVER (PARTITION BY articleid ORDER BY trandate) RowNum
FROM stock where ArticleID =@ArticleId),
/* CleanStock - A recursive CTE. This runs down the list of values for each stock, checking the Price column, if it is null it gets the previous non NULL value./
CleanStock
AS (SELECT articleid,
items,
WACRunningTotal,
ISNULL(WACPrice ,0) WACPrice ,/ Ensure we start with no NULL values for each stock /
trandate,
RowNum
FROM StockCTE cur
WHERE RowNum = 1
UNION ALL
SELECT Curr.articleid,
curr.items,
Curr.WACRunningTotal,
case when Curr.WACPrice=0 then prev.WACPrice else ((curr.WACPricecurr.Items)+(prev.WACRunningTotal*prev.WACPrice))/curr.WACRunningTotal end as WACPrice,
Curr.trandate,
Curr.RowNum
FROM StockCTE curr
INNER JOIN CleanStock prev ON curr.articleid = prev.articleid
AND curr.RowNum = prev.RowNum + 1)
/* Update the base table using the result set from the recursive CTE */
UPDATE trg
SET trg.WACPrice = src.WACPrice
FROM stock trg
INNER JOIN CleanStock src ON trg.articleid = src.articleid
AND trg.trandate = src.trandate and trg.ArticleID=@ArticleId
/* Display the results */
SELECT * FROM stock where ArticleID=@ArticleId order by TranDate
--drop table stock
end
This will yield result as
StockID ArticleID TranDate TranCode Items Price WACPrice WACRunningTotal
20119 10017 2009-01-06 10:37:40.000 IN 1088 27.91 27.91 1088
69802 10017 2009-01-20 00:40:44.000 OUT 39 0.00 27.91 1049
71338 10017 2009-01-20 10:42:25.000 OUT 967 0.00 27.91 82
91638 10017 2009-01-25 21:54:14.000 OUT 75 0.00 27.91 7
130881 10017 2009-02-05 14:38:34.000 IN 1061 312.18 310.3168 1068
174059 10017 2009-02-17 09:00:34.000 OUT 779 0.00 310.3168 289
188516 10017 2009-02-21 06:46:01.000 OUT 264 0.00 310.3168 25
192423 10017 2009-02-22 08:53:40.000 RET 8 0.00 310.3168 33
228070 10017 2009-03-04 02:24:26.000 OUT 30 0.00 310.3168 3
235671 10017 2009-03-06 03:59:49.000 IN 750 9.78 10.9773 753
247309 10017 2009-03-09 08:36:20.000 OUT 44 0.00 10.9773 709
249207 10017 2009-03-09 21:38:26.000 IN 256 155.09 49.2082 965
253665 10017 2009-03-11 02:42:14.000 OUT 379 0.00 49.2082 586
254121 10017 2009-03-11 05:59:00.000 OUT 527 0.00 49.2082 59
263772 10017 2009-03-13 20:46:09.000 OUT 11 0.00 49.2082 48
271272 10017 2009-03-15 22:09:04.000 OUT 34 0.00 49.2082 14
273709 10017 2009-03-16 13:51:34.000 OUT 1 0.00 49.2082 13
274065 10017 2009-03-16 16:13:02.000 OUT 5 0.00 49.2082 8
275679 10017 2009-03-17 02:38:20.000 IN 1165 217.19 216.0443 1173
280661 10017 2009-03-18 10:59:20.000 OUT 1053 0.00 216.0443 120
I am now working to find the COGS.
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