Consecutive Monthly Purchases SQL | Dataford Interview Questions

Write a SQL query to identify customers who made purchases in consecutive months for a Goldman Sachs dataset. Treat multiple purchases by the same customer within one calendar month as a single active month. Consecutive means adjacent calendar months, including across year boundaries.

Output

One row per qualifying customer.
Columns: customer_id, customer_name, consecutive_month_pairs, and first_consecutive_month.
Include only customers with at least one consecutive-month pair. Order by consecutive_month_pairs descending, then customer_id ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique Goldman Sachs customer identifier
customer_name	VARCHAR(100)	Customer's display name

purchases

Column	Type	Description
purchase_idPK	INT	Unique purchase identifier
customer_id	INT	Customer associated with the purchase
purchase_date	DATE	Date on which the purchase was recorded
amount	NUMERIC(12,2)	Purchase amount in dollars

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