Each of these queries offers a distinct piece of information about the database. Simply executing them in a vacuum offers very little insight. We have to look at the results of each to learn anything. In addition, all of the system catalog views only return statistics for the current database we're connected to.
If the PostgreSQL instance has dozens of databases and we're only connected to one, the statistics will only apply to that particular database. To obtain stats on every database in the instance, we would need to connect to each one and collect the information separately.
The first query returns the 20 largest tables in the database, including associated indexes and the The Oversize Attribute Storage Technique (TOAST ...
