Date-wise and bucket capacity-wise serial number - sql

Question

I couldn't give an appropriate title to my problem. Let me explain it through example.
Suppose I have the following table
INPUT
What I want
First, I want to group the transactions by date (dd-MM-yyyy)
Then I want to create a chunk/bucket of at most 2 items. Thus I want to assign a sub_batch_ref_id to each chunk/bucket of 2 items. In each chunk/bucket transactions must belong to exactly one date.
Convention of SUB_BATCH_REF_ID is BATCH_REF{global serial number of chunk/bucket}
A chunk or bucket can contain at most 2 items of the same date
I understand that this can be achieved through any high-level programming language (except data-oriented language like SQL) quite easily but I don't have such provision. The solution can be shaped into the following pseudocode for better understanding:
Pseudocode
//I have the following map (assumed)
Map<Date, List<Transaction>> dateWiseTransactions;
BUCKET_CAPACITY = 2
GLOBAL_SERIAL = 0
for each entry in dateWiseTransactions
LOOP
GLOBAL_SERIAL = GLOBAL_SERIAL + 1;
for each transaction in entry.value i.e. List<Transaction>
LOOP
if loopIndex > BUCKET_CAPACITY //loopIndex starts from 1
GLOBAL_SERIAL = GLOBAL_SERIAL + 1
end if;
transaction.SUB_BATCH_REF_ID = CONCAT(transaction.BATCH_REF, GLOBAL_SERIAL)
END LOOP;
END LOOP;
EXPECTED OUTPUT
What I tried
I tried to partition the transaction data by date first then assigned a row number but I couldn't come to a solution.
SELECT
T.*,
ROW_NUMBER() over (PARTITION BY TRUNC(INSERT_DATE) ORDER BY TRANSACTION_ID) rn
FROM TRANSACTION T
WHERE BATCH_REF='XYZ'
Any help is much appreciated.
SQL FIDDLE

Answer 1

This is not an optimal solution. Your actual problem is a rather complex graph problem -- because you want transactions only to be used once over all the dates.
One solution is to assign a "working" date to the transaction. The following does this randomly:
SELECT T.*
FROM (SELECT T.*,
ROW_NUMBER() over (PARTITION BY TRUNC(INSERT_DATE) ORDER BY TRANSACTION_ID) AS rn
FROM (SELECT T.*,
ROW_NUMBER() OVER (PARTITION BY BATCH_REF, TRANSACTION_ID ORDER BY DBMS_RANDOM.RANDOM) as seqnum
FROM TRANSACTION T
) T
WHERE BATCH_REF = 'XYZ' AND
SEQNUM = 1
) T
WHERE rn <= 2;