Top 10 Customers SQL | Dataford Interview Questions

Healthfirst Marketplace tracks member purchases in a transaction ledger. The analytics team needs the ten customer accounts with the highest cumulative purchase value.

Write a PostgreSQL query against member_purchase_transactions to return the top 10 customers by total purchase amount.

Requirements

Group all transactions by customer_name and calculate each customer's total purchase amount.
Sort totals from highest to lowest, place NULL totals last, and return only 10 rows. Use customer_name as a secondary ascending sort for deterministic ordering.

Schema

member_purchase_transactions

Column	Type	Description
transaction_idPK	INTEGER	Unique identifier for a marketplace purchase transaction.
customer_name	VARCHAR(100)	Name of the Healthfirst Marketplace customer account.
purchase_amount	NUMERIC(12,2)	Recorded purchase value. NULL represents an unpriced pending adjustment.
purchase_date	DATE	Date the transaction was recorded.

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