Detect Duplicate Records in SQL | Dataford Interview Questions

Finacle transaction ingestion can receive the same banking transaction more than once from core banking, ATM, or mobile channels. Write a PostgreSQL query to identify duplicate active records in finacle_transaction_ingest.

Requirements

Treat records as duplicates when customer_id, txn_reference, txn_date, amount, currency, and transaction_type match. A NULL reference must match another NULL reference.
Include only records with processing_status of POSTED or PENDING; exclude reversed records.
Return every duplicate record, its duplicate count, the customer name when available, and sort deterministically by customer, reference, date, and transaction ID.

Schema

finacle_transaction_ingest

Column	Type	Description
transaction_idPK	BIGINT	Unique ingested transaction record ID
customer_id	VARCHAR(20)	Finacle customer identifier
txn_reference	VARCHAR(40)	Source transaction reference
txn_date	DATE	Banking transaction date
amount	NUMERIC(14,2)	Transaction amount
currency	VARCHAR(3)	ISO currency code
transaction_type	VARCHAR(20)	Debit or credit
processing_status	VARCHAR(20)	Processing state
source_system	VARCHAR(20)	Originating channel or system

finacle_customers

Column	Type	Description
customer_idPK	VARCHAR(20)	Finacle customer identifier
customer_name	VARCHAR(120)	Customer display name
segment	VARCHAR(30)	Customer segment

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