Syntax
------

USE db_name

In MariaDB 11.3 one can also use

USE DATABASE db_name;

Description
-----------

The 'USE db_name' statement tells MariaDB to use the db_name database as the
default (current) database for subsequent statements. The database remains the
default until the end of the session or another USE statement is issued:

USE db1;
SELECT COUNT(*) FROM mytable;   # selects from db1.mytable
USE db2;
SELECT COUNT(*) FROM mytable;   # selects from db2.mytable

The DATABASE() function (SCHEMA() is a synonym) returns the default database.

Another way to set the default database is specifying its name at mariadb
command line client startup.

One cannot use USE DATABASE to a database one has no privileges to. The reason
is that a user with no privileges to a database should not be able to know if
a database exists or not.

URL: https://mariadb.com/kb/en/use-database/