Fetching records with slug instead of ID

Question

I'm currently trying to find the best way (in term of usability and performance) when dealing with a situation like fetching records tagged with a specific tag, or category, or something like that.

A good way (the way I wanted to do), would be to fetch records with the tag/category slug, so the URL would look like :

http://stackoverflow.com/questions/tagged/language-agnostic

fetching records by slug, which looks better than :

http://stackoverflow.com/questions/tag/789/language-agnostic

fetching by ID and adding the slug behind so it's more search-engine friendly. This one is better performance-wise, because fetching data by an integer ID would be faster than a string. (cmiiw)

Now, with a db schema like :

posts    post_to_tags    tags
-----    ------------    ----
id       id              id
title    post_id         name
content  tag_id          slug
...                      ...

am I doing it right ? Is there pitfall or best-practices that I need to know to avoid performance problems ? (eg. tags should not exceed 10,000 records, or tag slug should not exceed n characters, or something else)

Thanks in advance.

Answer 1

With the first URL style and your current db design, you can do this:

select ...
from   posts p
join   posts_to_tags pt on pt.post_id = p.post_id
join   tags t on t.id = pt.tag_id
where  t.slug = [url slug value];

As long as tags.slug is indexed, this should be very efficient, hardly any different from

select ...
from   posts p
join   posts_to_tags pt on pt.post_id = p.post_id
where  pt.tag_id = [url tag ID];

Answer 2

The first one is better, but can the slugs possibly be changed? In that case you'd need to have a redirect table (e.g. "some-article-about-dogs" is now "article-about-dogs-and-cats").