SQL and Postgres: simple schema that can be used as example

simple_schema.sql

DROP TABLE customers, invoices, items;

CREATE TABLE customers (
    customer_id SERIAL PRIMARY KEY,
    name TEXT NOT NULL UNIQUE
    );

CREATE TABLE invoices (
    invoice_id SERIAL PRIMARY KEY,
    customer_id BIGINT REFERENCES customers (customer_id)
    );

CREATE TABLE items (
    item_id SERIAL PRIMARY KEY,
    invoice_id BIGINT REFERENCES invoices (invoice_id),
    name TEXT NOT NULL
    );

https://www.crunchydata.com/blog/sql-tricks-for-more-effective-crud