Top Customers SQL With YoY | Dataford Interview Questions

Write a SQL query to identify the top 10% of customers by billing volume over the last quarter, including their year-over-year growth rate at LiveRamp.

Use July 15, 2025 as the reporting date, so the last completed quarter is April through June 2025. Compare each customer's billing volume with April through June 2024.

Output

One row per customer in the top billing decile.
Columns: customer_id, customer_name, current_quarter_billing, prior_year_billing, and yoy_growth_rate.
Return growth as a decimal, exclude customers outside the top decile, and order by current billing volume descending, then customer_id ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique LiveRamp customer identifier
customer_name	VARCHAR(150)	Customer display name

billing_transactions

Column	Type	Description
billing_idPK	INT	Unique billing transaction identifier
customer_id	INT	Customer associated with the billing transaction
billing_date	DATE	Date on which billing was recorded
billing_amount	NUMERIC(14,2)	Billing amount in US dollars
billing_reference	VARCHAR(40)	External billing reference

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Problem