CREATE TABLE item_types (
    id SERIAL PRIMARY KEY,
    item_type_name VARCHAR(50)
);

CREATE TABLE items (
    id SERIAL PRIMARY KEY,
    item_name VARCHAR(50),
    item_type_id INT,

    CONSTRAINT fk_items_item_types
    FOREIGN KEY (item_type_id)
    REFERENCES item_types(id)
);

CREATE TABLE cities (
    id SERIAL PRIMARY KEY,
    city_name VARCHAR(50)
);

CREATE TABLE customers (
    id SERIAL PRIMARY KEY,
    customer_name VARCHAR(100),
    birthday DATE,
    city_id INT,

    CONSTRAINT fk_customers_cities
    FOREIGN KEY (city_id)
    REFERENCES cities(id)
);

CREATE TABLE orders (
    id SERIAL PRIMARY KEY,
    customer_id INT,

    CONSTRAINT fk_orders_customers
    FOREIGN KEY (customer_id)
    REFERENCES customers(id)
);

CREATE TABLE order_items (
    order_id INT,
    item_id INT,

    CONSTRAINT pk_order_items
    PRIMARY KEY (order_id, item_id),

    CONSTRAINT fk_order_items_orders
    FOREIGN KEY (order_id)
    REFERENCES orders(id),

    CONSTRAINT fk_order_items_items
    FOREIGN KEY (item_id)
    REFERENCES items(id)
    
);