Detect Multiple Card Linking Attempts | Dataford Interview Questions

Write a query to identify users who have attempted to link more than three different payment cards to their Coinbase account within a rolling 24-hour window.

Return the earliest qualifying window for each user. Treat card-link attempts with valid user and payment-card records as eligible.

Output

One row per user with a qualifying window.
Columns: user_id, email, window_start, window_end, and different_card_count.
Order by user_id ascending, with one earliest qualifying window per user.

Schema

users

Column	Type	Description
user_idPK	INTEGER	Coinbase user identifier
email	VARCHAR(150)	User email address

payment_cards

Column	Type	Description
card_idPK	INTEGER	Payment card identifier
card_label	VARCHAR(80)	Masked card description

card_link_attempts

Column	Type	Description
attempt_idPK	INTEGER	Card-link attempt identifier
user_id	INTEGER	User who attempted the link
card_id	INTEGER	Card involved in the attempt
attempted_at	TIMESTAMP	Timestamp of the link attempt
attempt_status	VARCHAR(30)	Outcome of the link attempt

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Problem