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Checking vs. Savings: Where's the Money Moving?
mediumSQLJoinsGroupBy
Northline's product team is deciding whether to promote savings accounts harder.
customers
| id | name | account_type | city |
|---|---|---|---|
| 1 | Farah Idris | checking | Chicago |
| 2 | Grant Boyle | savings | Miami |
| 3 | Hana Suzuki | checking | Chicago |
| 4 | Ibrahim Njoku | savings | Miami |
| 5 | Jade Wu | checking | Seattle |
transactions
| id | customer_id | amount | type | txn_date |
|---|---|---|---|---|
| 1 | 1 | 500 | deposit | 2023-07-01 |
| 2 | 1 | -120 | withdrawal | 2023-07-03 |
| 3 | 2 | 1000 | deposit | 2023-07-02 |
| 4 | 2 | -300 | withdrawal | 2023-07-05 |
| 5 | 3 | 250 | deposit | 2023-07-04 |
| 6 | 3 | -600 | withdrawal | 2023-07-06 |
| 7 | 4 | 800 | deposit | 2023-07-07 |
| 8 | 4 | -450 | withdrawal | 2023-07-08 |
| 9 | 5 | 2000 | deposit | 2023-07-09 |
| 10 | 5 | -1500 | withdrawal | 2023-07-10 |
| 11 | 1 | -200 | transfer | 2023-07-11 |
| 12 | 3 | 400 | deposit | 2023-07-12 |
Task: Write a query that returns one row per account_type, with the net movement of money across every transaction belonging to a customer of that type (as net_amount), rows in alphabetical order of account_type.
Example output — shape only, on invented totals. A group that paid out more than it took in comes back negative.
| account_type | net_amount |
|---|---|
| checking | -240 |
| savings | 1875 |
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