I do not understand the question. All tables are external in the sense that they are stored on the MySQL server and not in SQLyog (the client).
With recent MySQL version there are 'federated' tables. refer to http://dev.mysql.com/doc/refman/5.1/en/federated-storage-engine.html
.. and also note that this need to be enabled in configuration with some MySQL versions. Ther is also a 'federatedX' 3rd party storage engine. This one is better maintained than the official 'federated' one but only ships with patched/unofficial servers like MariaDB.