After execution of the above commands, I create a table in schema "data_schema" using the "postgres" superuser. But I can't access the created table with user "loki"
Were all the above steps executed as "postgres", or was just the CREATE TABLE statement done as that user?
If it is all done as "postgres" superuser then it works for me. Your example ALTER DEFAULT PRIVILEGES without specifying the FOR ROLE only applies to objects created by the same user who executed the ALTER DEFAULT PRIVILEGES.
