PostgreSQL describes all database objects using the meta information stored in database relations. These relations hold information about tables, views, functions, indexes, foreign-data wrappers (FDWs), triggers, constraints, rules, users, groups, and so on. This information is stored in the pg_catalog schema, and to make it more readable by humans, PostgreSQL also provides the information_schema schema, in which the meta information is wrapped and organized into views.
In the psql client, users can see exactly what is happening behind the scenes when a certain meta command is executed, such as \z, by enabling ECHO_HIDDEN. The ECHO_HIDDEN or -E switch allows users to study the system catalog tables of PostgreSQL. You need to run the following command:
postgres=# \set ECHO_HIDDEN
postgres=# \d
********* QUERY **********
SELECT n.nspname as "Schema",
c...
