Change schema in Oracle

Even though I do it regularly, I always forget the commands.

To display the current user and the current schema:

SELECT sys_context('USERENV','SESSION_USER') as "USER NAME", sys_context('USERENV', 'CURRENT_SCHEMA') as "CURRENT SCHEMA" FROM dual;

To change the current schema, instead of prefixing the table names:

ALTER SESSION SET CURRENT_SCHEMA = hdm;