Typical Size by Type
Risk at Northline Bank is asking whether withdrawals here run bigger than deposits, and wants the typical signed amount for each kind of movement. Signed, deliberately: the report is meant to show direction as well as size, so an outflow arrives on the page as a negative number.
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 |
The table already exists in the database — there is nothing to create or load.
Task: Write a query that returns two columns, type and avg_amount, one row per transaction type, avg_amount being the mean amount of movements of that type exactly as stored — signs included — rounded to 2 decimal places. Highest value first; two types on the same figure come back in alphabetical order of type.
Example output — shape only, on invented averages. The type labels are the real stored ones, and the figures keep the sign the ledger gives them:
| type | avg_amount |
|---|---|
| deposit | 1240.5 |
| withdrawal | -305.75 |
| transfer | -880.25 |
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