Slugs - Help me to understand

[eluser]Mauricio de Abreu Antunes[/eluser]
Hello, i'm trying to understand slugs.

http://ericlbarnes.com/post/13129707173/...ug-library

This post tells me to insert my new with a slug like 'help-me-with-slugs'.
Ok, i understood this part. I can not understand how i can select data from a slug?

Code:

select * from news where slug = 'help-me-with-slugs';

Ok, i can get data from this, but when i insert a slug, it can be duplicated in the database. Is necessary to validate my title?

Btw,

Code:

...where slug = 'help-me-with-slugs'

is not so good to the database.
Performing a query with no primary key like http://www.site.com/news/24/help-me-with-slugs
where 24 is 'help-me-with-slugs' ID.

And what about routes if i get 'help-me-with-slugs' pagination?

Thanks!