Longest Gap Between Transactions | Dataford Interview Questions

Write a SQL query to find the longest gap between transactions for each customer. Use the transactions table and compare transaction dates for the same customer. Exclude customers with fewer than two valid transaction dates.

Output

One row per eligible customer with customer_id and longest_gap_days.
Return the maximum number of days between consecutive transaction dates.
Order results by customer_id ascending.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	VARCHAR(20)	Identifier of the customer making the transaction
transaction_date	DATE	Calendar date of the transaction

Whenever you're ready, walk me through your approach or go straight to the code. The requirements and the one table are in the Question tab.

Problem

Output

One row per eligible customer with customer_id and longest_gap_days.
Return the maximum number of days between consecutive transaction dates.
Order results by customer_id ascending.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
customer_id	VARCHAR(20)	Identifier of the customer making the transaction
transaction_date	DATE	Calendar date of the transaction

Whenever you're ready, walk me through your approach or go straight to the code. The requirements and the one table are in the Question tab.