Average Session Time by User | Dataford Interview Questions

Nielsen Digital Content Ratings analysts need to understand how long each user spends consuming digital content. A session is defined as the elapsed time between page_load and page_exit for a page view.

Write a PostgreSQL query that calculates the average completed session duration for every user.

Requirements

Use a CTE to calculate each valid session duration in seconds.
Exclude rows with a missing page_exit or with page_exit earlier than page_load.
Return every user, including users with no valid completed sessions. Represent their average as NULL.
Round average duration to two decimal places and order by user_id ascending.

Schema

users

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

page_sessions

Column	Type	Description
session_idPK	INTEGER	Unique page-view identifier
user_id	INTEGER	References users.user_id
page_url	TEXT	Page visited
page_load	TIMESTAMP	Page load timestamp
page_exit	TIMESTAMP	Page exit timestamp

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