Bigger Than Typical
The anomaly queue at Northline Bank holds movements that are unusually large for this ledger, and "unusually large" is not a number anybody wrote down — it is whatever the mean movement happens to be right now, recomputed as the ledger grows.
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 three columns — id, type and amount — for every movement whose amount is strictly greater than the mean amount across the whole ledger, taken as stored with signs included. Largest amount first; two movements on the same amount come back with the smaller id first.
Example output — shape only, on invented movements. Any type can qualify, so long as the stored amount clears the ledger-wide mean:
| id | type | amount |
|---|---|---|
| 47 | deposit | 9400 |
| 33 | deposit | 7100 |
| 51 | transfer | 6250 |
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