int mysql_select_db(string database_name, int [link_identifier] );
Returns: true on success, false on error
mysql_select_db() sets the current active database on the server that's associated with the specified link identifier. If no link identifier is specified, the last opened link is assumed. If no link is open, the function will try to establish a link as if mysql_connect() was called, and use it.
Every subsequent call to mysql_query() will be made on the active database.
For downward compatibility mysql_selectdb() can also be used.