Role "public" and Schema "public"
PostgreSQL中有两种public，角色public和public schema，不同使用场景使用不同的public，下面就这两种记录下。
role "public"
The key word PUBLIC indicates that the privileges are to be granted to all roles, including those that might be created later. PUBLIC can be thought of as an implicitly defined group that always includes all roles. Any particular role will have the sum of privileges granted directly to it, privileges granted to any role it is presently a member of, and privileges granted to PUBLIC.
From < https://www.postgresql.org/docs/current/sql-grant.html >
schema "public"
By default, users cannot access any objects in schemas they do not own. To allow that, the owner of the schema must grant the USAGE privilege on the schema. To allow users to make use of the objects in the schema, additional privileges might need to be granted, as appropriate for the object.
A user can also be allowed to create objects in someone else's schema. To allow that, the CREATE privilege on the schema needs to be granted. Note that by default, everyone has CREATE and USAGE privileges on the schema public. This allows all users that are able to connect to a given database to create objects in its public schema. Some usage patterns call for revoking that privilege:
REVOKE CREATE ON SCHEMA public FROM PUBLIC;
(The first “public” is the schema, the second “public”(public角色) means “every user”. In the first sense it is an identifier, in the second sense it is a key word, hence the different capitalization; recall the guidelines from Section 4.1.1.)
From < https://www.postgresql.org/docs/current/ddl-schemas.html#DDL-SCHEMAS-PATTERNS >
