How to do a complex calculation as this sample - sql

Question

In the stored procedure (I'm using SQL server2008), I'm having a business like this sample:
ID City Price Sold
1 A 10 3
1 B 10 5
1 A 10 1
1 B 10 3
1 C 10 5
1 C 10 2
2 A 10 1
2 B 10 6
2 A 10 3
2 B 10 4
2 C 10 3
2 C 10 4
What I want to do is:
with each ID, sort by City first.
After sort, for each row of this ID, re-calculate Sold from top to bottom with condition: total of Sold for each ID does not exceed Price (as the result below).
And the result like this:
ID City Price Sold_Calculated
1 A 10 3
1 A 10 1
1 B 10 5
1 B 10 1 (the last one equal '1': Total of Sold = Price)
1 C 10 0 (begin from this row, Sold = 0)
1 C 10 0
2 A 10 1
2 A 10 3
2 B 10 6
2 B 10 0 (begin from this row, Sold = 0)
2 C 10 0
2 C 10 0
And now, I'm using the Cursor to do this task: Get each ID, sort City, calculate Sold then, and save to temp table. After finish calculating, union all temp tables. But it take a long time.
What I know people advise is, DO NOT use Cursor.
So, with this task, can you give me the example (with using select form where group) to finish? or do we have other ways to solve it quickly?
I understand this task is not easy for you, but I still post here, hope that there is someone helps me to go through.
I'm very appriciated for your help.
Thanks.

Answer 1

In order to accomplish your task you'll need to calculate a running sum and use a case statement
Previously I used a JOIN to do the running sum and Lag with the case statement
However using a recursive Cte to calculate the running total as described here by Aaron Bertand, and the case statement by Andriy M we can construct the following, which should offer the best performance and doesn't need to "peek at the previous row"
WITH cte
AS (SELECT Row_number()
OVER ( partition BY id ORDER BY id, city, sold DESC) RN,
id,
city,
price,
sold
FROM table1),
rcte
AS (
--Anchor
SELECT rn,
id,
city,
price,
sold,
runningTotal = sold
FROM cte
WHERE rn = 1
--Recursion
UNION ALL
SELECT cte.rn,
cte.id,
cte.city,
cte.price,
cte.sold,
rcte.runningtotal + cte.sold
FROM cte
INNER JOIN rcte
ON cte.id = rcte.id
AND cte.rn = rcte.rn + 1)
SELECT id,
city,
price,
sold,
runningtotal,
rn,
CASE
WHEN runningtotal <= price THEN sold
WHEN runningtotal > price
AND runningtotal < price + sold THEN price + sold - runningtotal
ELSE 0
END Sold_Calculated
FROM rcte
ORDER BY id,
rn;
DEMO

Answer 2

As #Gordon Linoff commented, the order of sort is not clear from the question. For the purpose of this answer, I have assumed the sort order as city, sold.
select id, city, price, sold, running_sum,
lag_running_sum,
case when running_sum <= price then Sold
when running_sum > price and price > coalesce(lag_running_sum,0) then price - coalesce(lag_running_sum,0)
else 0
end calculated_sold
from
(
select id, city, price, sold,
sum(sold) over (partition by id order by city, sold
rows between unbounded preceding and current row) running_sum,
sum(sold) over (partition by id order by city, sold
rows between unbounded preceding and 1 preceding) lag_running_sum
from n_test
) n_test_running
order by id, city, sold;
Here is the demo for Oracle.
Let me break down the query.
I have used SUM as analytical function to calculate the running sum.
The first SUM, groups the rows based on id, and in each group orders the row by city and sold.
The rows between clause tell which rows to be considered for adding up. Here i have specified it to add
current row and all other rows above it. This gives the running sum.
The second one does the same thing except for, the current row is excluded from adding up. This
essentially creates a running sum but lagging the previous sum by one row.
Using this result as inline view, the outer select makes use of CASE statement to determine the
value of new column.
As long as the running sum is less than or equal to price it gives sold.
If it crosses the price, the value is adjusted so that sum becomes equal to price.
For the rest of the rows below it, value is set as 0.
Hope my explanation is quite clear.

Answer 3

To me, it sounds like you could use window functions in a case like this. Is this applicable?
Although in my case your end result would possibly look like:
ID City Price Sold_Calculated
2 A 10 4
2 B 10 6
2 C 10 0
Which could have an aggregation like
SUM(Sold_Calculated) OVER (PARTITION BY ID, City, Price, Sold_Calculated)
depending on how far down you want to go.. You could even use a case statement if need be

Answer 4

Are you looking to do this entirely in SQL? A simple approach would be this:
SELECT C.ID,
C.City,
C.Price,
calculate_Sold_Function(C.ID, C.Price) AS C.Sold_Calculated
FROM CITY_TABLE C
GROUP BY C.City
Where calculate_Sold_Function is a T-SQL/MySQL/etc function taking the ID and Price as parameters. No idea how you plan on calculating price.