If they're on the same mysql host (and you've got the appropriate permissions) you can access the tables by simply prefixing them with the schema name: otherdb.tablename. You can even run queries joining across the two databases.

If they're on a different server you'll need to add a separate connection and specify it as part of the query by using the $options['target'] setting.

If they're on the same mysql host (and you've got the appropriate permissions) you can access the tables by simply prefixing them with the schema name: otherdatabasename.tablename. You can even run queries joining across the two databases.

If they're on a different server you'll need to add a separate connection and specify it as part of the query by using the $options['target'] setting.