Top 3 Longest Sessions Per User | Dataford Interview Questions

Your question is Top 3 Longest Sessions Per User. Start with the requirements and the two tables on the right.

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Problem

Anduril operators use Lattice to monitor and coordinate activity across operational surfaces. The analytics team wants to identify the longest sessions for each user.

Write a PostgreSQL query that returns the top three completed sessions for every user, ranked by session duration.

Requirements

Calculate each completed session's duration in whole seconds from started_at and ended_at.
Rank sessions independently for each user, with the longest sessions ranked first. Break duration ties by the smaller session_id.
Return only ranks 1 through 3, including the user's name, session ID, Lattice surface, and duration.
Exclude sessions with a NULL ended_at value and users without completed sessions.

Schema

users

Column	Type	Description
user_idPK	INTEGER	Unique user identifier
user_name	VARCHAR(100)	Operator display name

session_logs

Column	Type	Description
session_idPK	INTEGER	Unique session identifier
user_id	INTEGER	References users.user_id
started_at	TIMESTAMPTZ	Session start timestamp
ended_at	TIMESTAMPTZ	Session end timestamp, or NULL while active
surface	VARCHAR(80)	Lattice surface used during the session