SQL Window Functions | Dataford Interview Questions

Your question is SQL Window Functions. Start with the requirements and the two tables on the right.

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Problem

Carvana's Product Analytics team wants to understand how shoppers move through vehicle detail pages during completed web sessions. Write a PostgreSQL query using LAG and LEAD to expose the previous and next action surrounding each vehicle view.

Requirements

Include only completed web sessions that started in January 2026.
Return one row for each vehicle_view event, including the previous event type, next event type, and seconds until the next event.
Partition the window calculations by session and order events chronologically, using event_id as a tie-breaker.
Preserve NULL when there is no previous or next event.

Schema

sessions

Column	Type	Description
session_idPK	VARCHAR(20)	Unique browsing session identifier
user_id	INT	Shopper identifier
platform	VARCHAR(20)	Product platform used during the session
session_status	VARCHAR(20)	Outcome of the browsing session
started_at	TIMESTAMP	Session start timestamp

vehicle_events

Column	Type	Description
event_idPK	INT	Unique event identifier
session_id	VARCHAR(20)	Session associated with the event
vehicle_id	VARCHAR(20)	Carvana vehicle associated with the event
event_type	VARCHAR(30)	Action recorded on the product surface
event_ts	TIMESTAMP	Event occurrence timestamp