Window Functions and Ranking | Dataford Interview Questions

Explain window functions. What is the difference between ROW_NUMBER(), RANK(), and DENSE_RANK()?

Using the provided payments table, calculate successful payment totals per account and currency, then apply all three ranking functions within each currency. Include a deterministic tie-breaker for ROW_NUMBER() and exclude unsuccessful or incomplete payments.

Output

One row per account and currency with currency, account_id, and total_amount
Include row_number_rank, rank_value, and dense_rank_value
Sort by currency, total_amount descending, and account_id ascending

Schema

payments

Column	Type	Description
payment_idPK	INT	Unique payment identifier
account_id	INT	Account associated with the payment
currency	VARCHAR(3)	Three-letter payment currency code
amount	DECIMAL(12,2)	Payment amount in the payment currency
status	VARCHAR(20)	Payment processing status

Your question is Window Functions and Ranking. Start with the requirements and the one table in the Question tab.

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Problem

Explain window functions. What is the difference between ROW_NUMBER(), RANK(), and DENSE_RANK()?

Output

One row per account and currency with currency, account_id, and total_amount
Include row_number_rank, rank_value, and dense_rank_value
Sort by currency, total_amount descending, and account_id ascending

Schema

payments

Column	Type	Description
payment_idPK	INT	Unique payment identifier
account_id	INT	Account associated with the payment
currency	VARCHAR(3)	Three-letter payment currency code
amount	DECIMAL(12,2)	Payment amount in the payment currency
status	VARCHAR(20)	Payment processing status

Your question is Window Functions and Ranking. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.