Calculating COGS to finish stock balance report SQL - sql

Question

I have two source table as following: Purchase & Sale
purchase (incoming)
--------------+----------+-------+----------+--------------
inventory_id | quantity | price | Amount | timestamp
--------------+----------+-------+----------+--------------
A | 1 | $1.00 | $1.00 | 2020-02-01
B | 2 | $1.00 | $2.00 | 2020-02-02
C | 4 | $2.00 | $8.00 | 2020-02-03
--------------+----------+-------+----------+--------------
sale (outgoing)
--------------+----------+-------+----------+--------------
inventory_id | quantity | price | Revenue | timestamp
--------------+----------+-------+----------+--------------
A | 1 | $3.00 | $3.00 | 2020-02-04
B | 1 | $3.00 | $3.00 | 2020-02-05
C | 2 | $3.00 | $6.00 | 2020-02-05
C | 1 | $3.00 | $3.00 | 2020-02-07
--------------+----------+-------+----------+--------------
What I want to do is the balance report in the below format:
Balance Report (2020-02-02 to 2020-02-05)
--------------+-----------+-------------+-------------+---------------+-----------+------------+---------+------------+
inventory_id | Begin Qty | Begin Amount| Purchase Qty|Purchase Amount| Sale Qty | COGS Amount | End Qty | End Amount |
--------------+-----------+-------------+-------------+---------------+-----------+------------+---------+------------+
A | 1 | $1.00 | | | 1 | $1.00 | | |
B | | | 2 | $2.00 | 1 | $1.00 | $1.00 | $1.00 |
C | | | 4 | $8.00 | 2 | $4.00 | $2.00 | $4.00 |
--------------+-----------+-------------+-------------+---------------+-----------+------------+---------+------------+
Note: The last outgoing transaction is out of the Report time range (2-05/02/2020) then not showing on the report.
MY CURRENT SOLUTION:
Add one column 'COGS' in the Sale table
I have to calculate the COGS of all inventory_id in the current sale order
Then save the COGS to the server with other information of sale order
THE PROBLEM:
If there is any change of the past transactions in the Purchase or Sale order, the COGS column does not UPDATE.
I NEED HELP ON:
Case 1: Keep COGS Column in the Sale table
How to update the value in this column if pasts transactions changed?
Case 2: Remove COGS Column
Pls help me to write a query to calculate the Sale Amount column in the Balance Report (Moving average is ok)
It would be great if you could provide the query to calculate the Sale Amount column by FIFO, LIFO.
Thanks a lot.

Answer 1

I found the solution: "I need to update COGS unit price for every transaction"
Following is the main code to update COGS
You might need to change something to adapt your case.
I know it is not the best solution but for my case it is ok.
create procedure update_COGS
as
update Sale
set
Sale.price = b.Aprice
from
Sale a
left join (select code, SUM(quantity) as quantity, sum(amount) as amount, SUM(amount)/nullif(sum(quantity),0) as Aprice from Purchase group by code) b
on a.code = b.code