USE DATABASE command on SQL PLUS ORACLE 11gr1

you can login into oracle using sqlplusw username/password@connect-string and then do a select * from v$database

use select instance_name from v$instance; to find out which database are you currently connected to

Even though they all use the same noun the term "database" is something completely different between MySQL (SQL Server) and Oracle.

Usually a MySQL database is mapped to a schema/user in Oracle. In Oracle there is a 1:1 relationship between schemas and users.

A "database" in Oracle refers to the complete installation (which is also named "instance"). As there is typically only a single instance/installation there is no sense in "switching a database" in Oracle.

The closest thing to "USE mydatabase" in Oracle would be to switch the current schema:

ALTER SESSION SET current_schema = other_user;

Then you can access all tables of other_user without prefixing them. This of course requires your current user to have at least select privileges on the tables of the other user (i.e schema)