Hi @alex23
Are you sure you've connected to the correct database? There's plenty of interesting things 
Have a look here for some examples: Metabase Metadata SQL
The application database schema is mostly documented in the migration yaml:
https://github.com/metabase/metabase/blob/master/resources/migrations/000_migrations.yaml
And then there's a slightly outdated version here: https://github.com/metabase/metabase/wiki/Metabase-Database-Models