Querying Transactions in SQL | Dataford Interview Questions

Business Context

Shopify Financial Operations needs a monthly view of Shopify Payments activity by merchant for Q1 2025. The report should distinguish settled sales from settled refunds and exclude failed or pending transactions.

Task

Write a PostgreSQL query that joins payment_transactions to shopify_merchants and returns one row per merchant and transaction month.

Requirements

Include only transactions processed from January 1 through March 31, 2025 with status = 'settled'.
Calculate settled sale count, settled transaction count, gross sales, refund amount, net sales, and refund rate as a percentage of gross sales.
Include merchant name and plan, and sort by transaction month followed by merchant name.
Return a NULL refund rate when gross sales are zero.

Schema

shopify_merchants

Column	Type	Description
merchant_idPK	INT	Unique Shopify merchant identifier
merchant_name	VARCHAR(100)	Merchant display name
plan	VARCHAR(30)	Shopify subscription plan

payment_transactions

Column	Type	Description
transaction_idPK	INT	Unique payment transaction identifier
merchant_id	INT	Merchant associated with the transaction
order_id	VARCHAR(30)	Shopify order reference
transaction_type	VARCHAR(20)	Payment transaction type
status	VARCHAR(20)	Transaction processing status
amount	DECIMAL(12,2)	Transaction amount in the reporting currency
processed_at	DATE	Date the transaction was processed

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