Sets the current active database on the server that's associated with the
specified link identifier. Every subsequent call to
mysql_query() will be made on the active database.
Parameters
database_name
The name of the database that is to be selected.
link_identifier
The MySQL connection. If the
link identifier is not specified, the last link opened by
mysql_connect() is assumed. If no such link is found, it
will try to create one as if mysql_connect() was called
with no arguments. If by chance no connection is found or established, an
E_WARNING level warning is generated.