Pagila
The Pagila
database is a particularly interesting sample because it showcases many advanced PostgreSQL features. It relies heavily on stored procedures and even partitions some of its data. The main reason it's not used for examples here is because it's very small, only a few megabytes in size. The non-free license on the documentation for the original database it's based on (Sakila, a part of MySQL) makes it problematic to quote from here too.