Trade Within 24 Hours | Dataford Interview Questions

Vanguard Brokerage wants to measure how often users place a trade shortly after accessing their account. Write a PostgreSQL query to calculate the percentage of distinct users who completed at least one trade within 24 hours of any login.

Treat the 24-hour boundary as inclusive. A user should be counted only once, even if they have multiple qualifying logins or trades. Users with logins but no qualifying trade must remain in the denominator.

Requirements

Identify the distinct users who logged in.
Identify users with at least one trade occurring from the login timestamp through 24 hours afterward.
Return the qualifying-user count, total logged-in-user count, and percentage rounded to two decimal places.
Exclude trades that occurred before login or more than 24 hours after login.

Schema

logins

Column	Type	Description
login_idPK	INTEGER	Unique login event identifier
user_id	INTEGER	Vanguard user identifier
login_at	TIMESTAMP	Timestamp when the user logged in

trades

Column	Type	Description
trade_idPK	INTEGER	Unique trade identifier
user_id	INTEGER	User who placed the trade
traded_at	TIMESTAMP	Trade execution timestamp

Your question is Trade Within 24 Hours. Start with the requirements and the two tables in the Question tab.

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