We had a discussion today about the uniqueness of UUIDs (or GUID). In case you didn't know, according to Wikipedia, a UUID is:

"an identifier standard used in software construction, standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE)."

The uniqueness of a UUID is 1 2^¹²⁸. Now this doesn't really mean much to most people so the part I found particularly interesting is the uniqueness in terms we can try to understand. From Stackoverflow:

"consider the observable universe, which contains about 5×10^22 stars; every star could then have 6.8×10^15 universally unique GUIDs."

Wow.

Here's another way to write the probability:

1 in 340,000,000,000,000,000,000,000,000,000,000,000,000

or

"In other words, only after generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. The probability of one duplicate would be about 50% if every person on earth owns 600 million UUIDs."

Stop and think about that for a second.

This raises the question. Given the fact they basically are unique, should we use them for a primary key instead of auto-incrementing in a database? There are good reasons to use either as a primary key.

Which do you use and why?

I recently made an update to a table and start receiving a weird error:

even though the SQL hadn't changed and I had only added a column to the database. Well, it turns out that cfqueryparam and ColdFusion do some weird caching that was causing the error. If changed the query (i.e. change the order of the WHERE statements (which didn't change the results)), the error went away.

Truly a weird error.

I recently ran into a situation where I needed to get the primary key of a table, knowing only the table name. Using the following code, you can pass it a table name, and it will return the primary key: