SQL Top Spenders by Month | Dataford Interview Questions

TikTok Shop needs a monthly leaderboard of its highest-spending users. Write a PostgreSQL query that returns the top three users by completed purchase spend for each calendar month.

Requirements

Join users to transactions using user_id.
Include only transactions with status = 'completed' and non-null amounts.
Aggregate spending by calendar month and user, then rank users within each month by total spend descending. Break ties with the smaller user_id.
Return up to three users per month, ordered chronologically and then by rank.

Schema

users

Column	Type	Description
user_idPK	INTEGER	Unique user identifier
display_name	VARCHAR(100)	User-facing display name
email	VARCHAR(255)	User email address

transactions

Column	Type	Description
transaction_idPK	INTEGER	Unique transaction identifier
user_id	INTEGER	User associated with the transaction
purchased_at	TIMESTAMP	Timestamp when the purchase occurred
amount	NUMERIC(12,2)	Purchase amount
status	VARCHAR(20)	Transaction processing status

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