A production-shaped e-commerce schema: products with variants, inventory per location, carts, orders with snapshotted line items, payments and shipments. Open it in the editor or export SQL for six dialects.
Bin-level inventory done properly: warehouses and storage locations, lot tracking for recalls, an append-only stock movement log with derived stock levels, purchase orders and outbound shipments.
A double-entry bank ledger: accounts in a single currency each, balanced journal entries that are never updated, card authorizations that hold funds, transfers kept separate from postings, and frozen statements.
A reservation system that actually handles availability: room types versus rooms, rate plans, a per-night rate and inventory calendar, reservations broken down by night, payments and verified reviews.
How a marketplace models many sellers listing the same product: a shared catalogue, competing offers, the buy box decision as a log, orders split into per-seller sub-orders, fulfilment, payouts and product-level reviews.