sql query for fifo inventory - sql

Question

I'm having trouble with a simple problem for fifo sql query (to calculate profit for each sales day).
There are two tables Production and Invoice. For each day of sales, I have to output total sales profit by using FIFO method.
Example, for second day profit , I have to use leftover item from previous day with their respecting price.
Here is the tables and desired output result
CREATE TABLE Production
(
id int identity(1,1) primary key,
Productid varchar(10),
pdate date,
Qty int,
Price decimal(18, 2),
);
INSERT INTO Production (Productid,pDate, Qty ,Price) VALUES ('PD1', '01/01/2017', 8, 200);
INSERT INTO Production (Productid,pDate ,Qty ,Price) VALUES ('PD2', '02/01/2017', 14, 300);
INSERT INTO Production (Productid,pDate ,Qty ,Price) VALUES ('PD3', '03/01/2017', 15, 150);
CREATE TABLE Sales
(
id int identity(1,1) primary key,
Sid varchar(10),
sDate date,
Productid varchar(10),
Qty int,
);
INSERT INTO Sales (Sid,sDate ,Productid ,Qty) VALUES ('S001', '04/01/2017', 'PD1', 5);
INSERT INTO Sales (Sid,sDate ,Productid ,Qty) VALUES ('S002', '05/01/2019', 'PD2', 4);
INSERT INTO Sales (Sid,sDate ,Productid ,Qty) VALUES ('S003', '06/01/2019', 'PD3', 6);
Manual calculation for leftover formula for each day
( existing - sales qty ) + purchase qty = leftover

Answer 1

I think a simple check on sales.qty < purchase.qty won't work. Since even if you have sales.qty < purchase.qty but have leftovers from last day then you will be using those leftovers first.
You should use try this:
with cte as(
select s.id,s.Sid,sDate,s.Productid,s.qty AS Qty,s.qty as saleqty,p.qty as productqty,p.price
,sum(p.qty-s.qty) over (order by sdate) as leftover
from purchase P
inner join sales S
on p.productid=s.productid
and p.pdate=s.sdate
)
select id, Sid,sDate,Productid,Qty,
case when lag(leftover) over (order by sdate)>0 then lag(leftover *price) over( order by sdate)
+( saleqty-lag(leftover) over (order by sdate)) * price
else saleqty * price end as profit
from cte;

Answer 2

Hope this would help.
SELECT
s.sid,
s.sdate,
p.productid,
s.qty,
CASE
WHEN s.qty <= p.qty
THEN s.qty*p.price
ELSE p.qty*p.price + (s.qty-p.qty) * (SELECT price FROM purchase WHERE pdate IN (SELECT MAX(pdate) FROM purchase WHERE pdate < s.sdate))
END AS PROFIT
FROM purchase p
JOIN sales s
ON p.productid = s.productid
AND p.pdate = s.sdate