In order to work with this example, you have to download and install PostgreSQL, in case you aren't already running it in your development computer or in a development server. PostgreSQL is available on multiple platforms and offers versions for Linux, macOS and Windows, among other operating systems. You can download and install this relational database management system from the
Download section of its web page: http://www.postgresql.org.
The next samples that work with a PostgreSQL database have been tested in PostgreSQL versions 9.6.x and PostgreSQL 10.x. Make sure you work with any of these versions.
There are interactive installers built by EnterpriseDB and BigSQL for macOS and Windows. In case you are working with macOS, Postgres.app provides a really easy way to install and use PostgreSQL on this operating system. You can read more about Postgres.app and download it from its web page: http://postgresapp.com.
After you finish the installation process, you have to...