Checking vs Savings Behavior
Northline Bank wants to know whether checking and savings customers behave differently, measured by how much money they push through the bank in total — in either direction, since a customer moving 2000 in and 1500 out is busy, not quiet.
transactions — one row per movement of money. customer_id points at a row in customers; type is one of deposit, withdrawal or transfer; txn_date is the day it settled. The ledger is signed: money arriving in an account is stored as a positive amount, and money leaving it as a negative one, so a 600-dollar withdrawal is recorded as -600.
| 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 |
customers — one row per account holder at Northline. account_type is either checking or savings; city is the branch city the account belongs to.
| 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 |
Both tables already exist in the database — there is nothing to create or load.
Task: Write a query that returns two columns, account_type and volume, one row per account type with any movements, volume being the total money moved by that type's customers ignoring direction, rounded to 2 decimal places. Largest volume first.
Example output — shape only, on invented totals. The account_type labels are the real stored ones:
| account_type | volume |
|---|---|
| savings | 18400 |
| checking | 9600 |
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