I've looked around and seen the way to create your own url shortener/mapping is by using an auto increment PK, convert it to base62 to use as the short_key, and then use the key to access the long_url value on queries. If I could set the short_code to be the PK, I would essentially gain a free index.
Is there a conversion that can shorten a string url (eg www.news.google.com#top) to a <6 character alphanumeric short_code that will be reliably unique?