SQL From Easy to Hard | Dataford Interview Questions

How would you demonstrate your SQL skills from easy to hard problems?

Use the provided tables to produce a progressively realistic analytical result involving users, fee tiers, and Spot trading activity. Include only filled trades executed during January 2025, while retaining users with no qualifying trades.

Output

One row per user, with user_id, tier_name, total_volume, and volume_rank
total_volume is the user's January filled-trade quote volume, with zero for no qualifying trades
Ranks restart for each tier, with tied volumes sharing a rank
Sort by tier_name, volume_rank, then user_id

Schema

users

Column	Type	Description
user_idPK	INT	Unique user identifier
fee_tier_id	INT	User's fee tier
country	VARCHAR(2)	Two-letter country code
signup_date	DATE	Date the user registered

fee_tiers

Column	Type	Description
tier_idPK	INT	Unique fee tier identifier
tier_name	VARCHAR(30)	Fee tier label
fee_rate	DECIMAL(8,6)	Trading fee rate

trades

Column	Type	Description
trade_idPK	INT	Unique trade identifier
user_id	INT	User who initiated the trade
symbol	VARCHAR(20)	Spot trading pair
quote_amount	DECIMAL(18,2)	Trade value in the quote asset
trade_status	VARCHAR(20)	Trade processing status
executed_at	DATE	Trade execution date

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