In some cases you can do things with a subquery that can't be done with join. However when using subqueries, there can be performance costs.
By placing a robots.txt file in your root directory you can easily prevent robots from accessing your website. This file can be easily created using simple text editors like Notepad in Windows or TextEdit in Mac OSX.
If you still can’t set your preferred domain, then read on to find out how to fix this error. The fix is quiet easy. You’ll simply need to add and verify your site once with www and once without it,