SQL Left Join for Inactive Customers | Dataford Interview Questions

Write a SQL query using a left join to identify customers who have not made a transaction in the last 90 days.

Use the provided customers and transactions tables. For deterministic evaluation, treat 2025-04-01 as the as-of date and include the boundary date.

Output

Return one row per qualifying customer.
Include customer_id and customer_name.
Include customers with no transactions and customers without a transaction from 2025-01-01 through 2025-04-01.
Sort by customer_id ascending.

Schema

customers

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

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	INT	Customer associated with the transaction
transaction_date	DATE	Date the transaction occurred
amount	DECIMAL(10,2)	Transaction amount

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