Net Profit per Trading Card

Problem

A collector resells trading cards. Every transaction is logged: a `purchase` records money spent acquiring a card, a `resale` records money received when selling it. Each card may be bought and sold many times.

Table: `card_trades`

| Column | Type |
|-------------|---------|
| card_name | varchar |
| action | text |
| trade_day | int |
| amount | int |

`(card_name, trade_day)` is the primary key. `action` is either `'purchase'` or `'resale'`. `amount` is the money for that single transaction.

The **net profit** of a card is the total received from resales minus the total spent on purchases, summed over all its transactions. A negative value means an overall loss.

Write a query that reports `card_name` and `net_profit` for each card. Return the rows in any order.

Tables

Example rows — the live problem includes the full dataset.

Expected output

Your answer should return 3 rows with the columns card_name, net_profit.

Starter code (SQL)

SELECT *
FROM card_trades;

Related SQL questions

• 3-Day Tweet Rolling AverageMedium
• 7-Day vs 28-Day Rolling Avg DivergenceMedium
• A/B Test Sample Ratio Mismatch (SRM) CheckMedium
• Accounts Streaming From Two Devices at OnceMedium
• Ad Campaign Funnel AnalysisMedium
• Agent Resolution RateMedium