Running Total Top Three Days | Dataford Interview Questions

Write a query using SQL window functions to calculate the running total revenue per merchant and identify their top 3 highest-grossing days.

Use completed transactions only. Treat NULL revenue as zero when calculating daily revenue, and aggregate multiple transactions for the same merchant and date.

Output

One row per merchant-day included in that merchant's top three days.
Columns: merchant_name, sale_date, daily_revenue, running_total, and top_day_rank.
Rank days by daily revenue descending, breaking ties by date ascending. Order the final result by merchant name and rank.

Schema

merchants

Column	Type	Description
merchant_idPK	INT	Unique merchant identifier
merchant_name	VARCHAR(100)	Merchant display name

merchant_transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
merchant_id	INT	Merchant receiving the transaction
sale_date	DATE	Calendar date of the transaction
revenue	DECIMAL(12,2)	Revenue generated by the transaction
status	VARCHAR(20)	Transaction processing status

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Problem