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Money Going Out

easySQLFilteringAggregation

The same liquidity report at Northline Bank needs the outflow line beside the inflow line, and the desk wants both printed as positive figures so the two can be read side by side without anybody doing sign arithmetic in their head. The ledger does not store them that way.

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Task: Write a query that returns exactly one row with one column, total_withdrawals, holding the total amount withdrawn as a positive number, rounded to 2 decimal places. Transfers are not withdrawals and must not be included.

Example output — the shape, on an invented figure. Note the sign: money out is reported as a positive figure, so a quarter of six thousand one hundred and twenty dollars leaving the bank reads:

total_withdrawals
6120

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