Second-Highest Per Merchant | Dataford Interview Questions

Write a query to find the second-highest transaction amount for each merchant using window functions.

Use the transactions table. Treat the second-highest amount as the second distinct highest value, and exclude merchants without at least two distinct non-null amounts.

Output

Return one row per qualifying merchant with merchant_id and second_highest_amount.
Sort by merchant_id in ascending order.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
merchant_id	VARCHAR(20)	Identifier of the merchant
amount	NUMERIC(12,2)	Transaction amount

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