Average Time to First Discovery | Dataford Interview Questions

Given a table of user DNA activation dates and subsequent login dates, write a query to find the average time to first discovery.

Treat the first discovery as the earliest login on or after the user's DNA activation date. Users without a qualifying login, and rows with NULL activation or login dates, are ignored.

Output

Return one row with average_time_to_first_discovery_days.
Report the average elapsed time in days, rounded to two decimal places.

Schema

user_dna_activations

Column	Type	Description
user_idPK	INT	Unique identifier for the user
activation_date	DATE	Date the user activated their DNA kit

user_logins

Column	Type	Description
login_idPK	INT	Unique identifier for the login event
user_id	INT	User associated with the login
login_date	DATE	Date of the login event

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Problem