Answer SQL Questions From a Schema | Dataford Interview Questions

Given the schema, ask some SQL questions.

Write a PostgreSQL query that summarizes payments during Q1 2025 for active merchants. Include merchants with no successful payments during the period, and exclude failed, pending, and out-of-period payments.

Output

One row per active merchant with merchant_id, merchant_name, successful_payment_count, and successful_volume.
Include zero values for merchants without qualifying payments.
Order by successful_volume descending, then merchant_id ascending.

Schema

merchants

Column	Type	Description
merchant_idPK	INT	Unique merchant identifier
merchant_name	VARCHAR(120)	Merchant display name
is_active	BOOLEAN	Whether the merchant is currently active

payments

Column	Type	Description
payment_idPK	INT	Unique payment identifier
merchant_id	INT	Merchant associated with the payment
status	VARCHAR(20)	Payment processing status
amount	NUMERIC(12,2)	Payment amount in the stated currency
currency	VARCHAR(3)	Three-letter payment currency
occurred_at	TIMESTAMP	Payment creation timestamp

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Problem