Window Functions for Data Quality | Dataford Interview Questions

Write a SQL query using window functions to identify duplicate records or calculate running totals.

For this exercise, calculate running posted transaction totals for each account. Include only transactions linked to an account and sort each account's results chronologically, using transaction ID to break date ties.

Output

One row per included transaction with account_id, account_name, transaction_id, transaction_date, amount, and running_total.
Include only posted transactions linked to an account.
Order by account_id, transaction_date, and transaction_id.

Schema

accounts

Column	Type	Description
account_idPK	INT	Unique account identifier
account_name	VARCHAR(100)	Display name of the account
account_type	VARCHAR(30)	Account classification

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
account_id	INT	Referenced account identifier
transaction_date	DATE	Date of the transaction
amount	NUMERIC(12,2)	Transaction amount
status	VARCHAR(20)	Transaction processing status

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