HardFinance18 min

Monthly net from the ledger

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Challenge

Subtract posted expenses from posted sales revenue for each month that has both.

Business context

The flash report defines net as posted sales credits minus posted expense debits. Voided lines are ignored, and mixed-case statuses still count as posted.

Instructions

Return month, revenue_cents, expense_cents, and net_cents. month is YYYY-MM. Revenue is posted credits to the revenue account. Expenses are posted debits to expense accounts. Keep months present in both totals. Sort by month.

Schema

accounts

id INTEGER · primary key
name TEXT
account_type TEXT · asset, liability, revenue, expense

vendors

id INTEGER · primary key
name TEXT · may include extra spaces
category TEXT · nullable

bills

id INTEGER · primary key
vendor_id INTEGER
amount_cents INTEGER
issued_on TEXT
due_on TEXT
paid_on TEXT · nullable
status TEXT · paid, open, void

ledger

id INTEGER · primary key
account_id INTEGER
txn_date TEXT
amount_cents INTEGER
direction TEXT · debit or credit
memo TEXT · nullable, may include extra spaces
status TEXT · mixed case: posted, Posted, POSTED, void

Sample rows

accounts
id	name	account_type
1	Cash	asset
2	Accounts Payable	liability
3	Sales Revenue	revenue

vendors
id	name	category
1	Harbor Office	Facilities
2	Northwind Cloud	Software
3	City Clinic Supplies	Medical

bills
id	vendor_id	amount_cents	issued_on	due_on	paid_on	status
1	1	180000	2025-01-02	2025-01-31	2025-01-20	paid
2	2	42000	2025-01-05	2025-02-04	2025-02-10	paid
3	2	42000	2025-02-05	2025-03-07	NULL	open

ledger
id	account_id	txn_date	amount_cents	direction	memo	status
1	4	2025-01-20	180000	debit	January rent	posted
2	5	2025-02-10	42000	debit	Cloud january	Posted
3	6	2025-01-28	250000	debit	Payroll	POSTED

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Next exercise: Second-highest product price