How to create BigQuery this query in retail dataset - sql

Question

I have a table with user retail transactions. It includes sales and cancels. If Qty is positive - it sells, if negative - cancels. I want to attach cancels to the most appropriate sell. So, I have tables likes that:
| CustomerId | StockId | Qty | Date |
|--------------+-----------+-------+------------|
| 1 | 100 | 50 | 2020-01-01 |
| 1 | 100 | -10 | 2020-01-10 |
| 1 | 100 | 60 | 2020-02-10 |
| 1 | 100 | -20 | 2020-02-10 |
| 1 | 100 | 200 | 2020-03-01 |
| 1 | 100 | 10 | 2020-03-05 |
| 1 | 100 | -90 | 2020-03-10 |
User with ID 1 has the following actions: buy 50 -> return 10 -> buy 60 -> return 20 -> buy 200 -> buy 10 - return 90. For each cancel row (with negative Qty) I find the previous row (by Date) with positive Qty and greater than cancel Qty.
So I need to create BigQuery queries to create table likes this:
| CustomerId | StockId | Qty | Date | CancelQty |
|--------------+-----------+-------+------------+-------------|
| 1 | 100 | 50 | 2020-01-01 | -10 |
| 1 | 100 | 60 | 2020-02-10 | -20 |
| 1 | 100 | 200 | 2020-03-01 | -90 |
| 1 | 100 | 10 | 2020-03-05 | 0 |
Does anybody help me with these queries? I have created one candidate query (split cancel and sales, join them, and do some staff for removing), but it works incorrectly in the above case.
I use BigQuery, so any BQ SQL features could be applied.
Any ideas will be helpful.

Answer 1

You can use the following query.
;WITH result AS (
select t1.*,t2.Qty as cQty,t2.Date as Date_t2 from
(select *,ROW_NUMBER() OVER (ORDER BY qty DESC) AS [ROW NUMBER] from Test) t1
join
(select *,ROW_NUMBER() OVER (ORDER BY qty) AS [ROW NUMBER] from Test) t2
on t1.[ROW NUMBER] = t2.[ROW NUMBER]
)
select CustomerId,StockId,Qty,Date,ISNULL(cQty, 0) As CancelQty,Date_t2
from (select CustomerId,StockId,Qty,Date,case
when cQty < 0 then cQty
else NULL
end AS cQty,
case
when cQty < 0 then Date_t2
else NULL
end AS Date_t2 from result) t
where qty > 0
order by cQty desc
result: https://dbfiddle.uk

Answer 2

You can do this as a gaps-and-islands problem. Basically, add a grouping column to the rows based on a cumulative reverse count of negative values. Then within each group, choose the first row where the sum is positive. So:
select t.* (except cancelqty, grp),
(case when min(case when cancelqty + qty >= 0 then date end) over (partition by customerid grp) = date
then cancelqty
else 0
end) as cancelqty
from (select t.*,
min(cancelqty) over (partition by customerid, grp) as cancelqty
from (select t.*,
countif(qty < 0) over (partition by customerid order by date desc) as grp
from transactions t
) t
from t
) t;
Note: This works for the data you have provided. However, there may be complicated scenarios where this does not work. In fact, I don't think there is a simple optimal solution assuming that the returns are not connected to the original sales. I would suggest that you fix the data model so you record where the returns come from.

Answer 3

The below query seems to satisfy the conditions and the output mentioned.The solution is based on mapping the base table (t) and having the corresponding canceled qty row alongside from same table(t1)
First, a self join based on the customer and StockId is done since they need to correspond to the same customer and product.
Additionally, we are bringing in the canceled transactions t1 that happened after the base row in table t t.Dt<=t1.Dt and to ensure this is a negative qty t1.Qty<0 clause is added
Further we cannot attribute the canceled qty if they are less than the Original Qty. Therefore I am checking if the positive is greater than the canceled qty. This is done by adding a '-' sign to the cancel qty so that they can be compared easily. -(t1.Qty)<=t.Qty
After the Join, we are interested only in the positive qty, so adding a where clause to filter the other rows from the base table t with canceled quantities t.Qty>0.
Now we have the table joined to every other canceled qty row which is less than the transaction date. For example, the Qty 50 can have all the canceled qty mapped to it but we are interested only in the immediate one came after. So we first group all the base quantity values and then choose the date of the canceled Qty that came in first in the Having clause condition HAVING IFNULL(t1.dt, '0')=MIN(IFNULL(t1.dt, '0'))
Finally we get the rows we need and we can exclude the last column if required using an outer select query
SELECT t.CustomerId,t.StockId,t.Qty,t.Dt,IFNULL(t1.Qty, 0) CancelQty
,t1.dt dt_t1
FROM tbl t
LEFT JOIN tbl t1 ON t.CustomerId=t1.CustomerId AND
t.StockId=t1.StockId
AND t.Dt<=t1.Dt AND t1.Qty<0 AND -(t1.Qty)<=t.Qty
WHERE t.Qty>0
GROUP BY 1,2,3,4
HAVING IFNULL(t1.dt, '0')=MIN(IFNULL(t1.dt, '0'))
ORDER BY 1,2,4,3
fiddle

Answer 4

Consider below approach
with sales as (
select * from `project.dataset.table` where Qty > 0
), cancels as (
select * from `project.dataset.table` where Qty < 0
)
select any_value(s).*,
ifnull(array_agg(c.Qty order by c.Date limit 1)[offset(0)], 0) as CancelQty
from sales s
left join cancels c
on s.CustomerId = c.CustomerId
and s.StockId = c.StockId
and s.Date <= c.Date
and s.Qty > abs(c.Qty)
group by format('%t', s)
if applied to sample data in your question - output is