erDiagram
    CUSTOMER ||--o{ CUSTOMER_ORDER : places
    CUSTOMER_ORDER ||--|{ ORDER_ITEM : includes
    PRODUCT ||--o{ ORDER_ITEM : referenced
    CUSTOMER_ORDER {
        int order_id PK
        int customer_id FK
    }
    ORDER_ITEM {
        int item_id PK
        int order_id FK
        int product_id FK
        int quantity
        decimal unit_price
    }