get-seller-balance.sql

select sum(transactions.price) from sellers
	left join products on products.seller_id = sellers.id
	left join purchases on purchases.product_id = products.id
	left join transactions on transactions.purchase_id = purchases.id
	where sellers.id = SELLER_ID and
		transactions.is_payed = 0 and
		transactions.date <= date_sub(now(), interval 1 week)