3+ Purchases on First and Last Day | Dataford Interview Questions

Find customers who purchased 3 or more books on both the first and last day of sales, excluding those with only one transaction.

Use the provided customer, book, and book-sales data. Treat a book's quantity as the number purchased and count distinct transaction IDs.

Output

One row per qualifying customer with customer_id, customer_name, first_day_books, last_day_books, and transaction_count.
Include only customers meeting both daily thresholds and having more than one transaction.
Order by customer_id ascending.

customers

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

books

Column	Type	Description
book_idPK	INT	Unique book identifier
title	VARCHAR(200)	Book title

book_sales

Column	Type	Description
sale_line_idPK	INT	Unique sales line identifier
transaction_id	INT	Transaction identifier, shared by multiple book lines
customer_id	INT	Purchasing customer
book_id	INT	Purchased book
sale_date	DATE	Date of the transaction
quantity	INT	Number of copies purchased

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