Use SQL commands such as INSERT and SELECT to query a readable external table, the same way that you query a regular database table. For example, to load travel expense data from an external table, ext_expenses, into a database table, expenses_travel:

=# INSERT INTO expenses_travel 
    SELECT * from ext_expenses where category='travel';

To load all data into a new database table:

=# CREATE TABLE expenses AS SELECT * from ext_expenses;