Joe Celko defends the honor of First Normal Form:
You do not need a complete understanding of regular expressions or ICD codes to follow this article, so don’t worry too much about it. The reason for posting the simplified regular expression was to scare you. My point was that this regular expression would be a pretty impressive
CHECK constraint on this column. Shall we be honest? Despite the fact that we know the best programming practice is to detect an error as soon as possible, do you believe that the original poster wrote such a constraint for the concatenated list of ICD codes?
I’m willing to bet that any such validation is being done in an input tier by some poor lonely program, in an application language. Even more likely, it’s not being done at all.
First Normal Form (1NF) says that this concatenated string is a repeated group, and we need to replace it with a proper relational construct.
In the meantime, I’ve continued my series on database normalization and call First Normal Form overrated:
In this video, we start at the ground floor with 1st Normal Form. We’ll learn what people think it is, what it really is, and why it’s not as great as it’s cracked up to be.
I agree with Joe that his ICD-10 code example is a bad database design. The area in which I don’t agree—and for this, I’m leaning heavily on C.J. Date—is that repeating groups actually violate 1NF. My video covers this in a bit more detail and I also include a quotation from Date’s recent book on database design talking about how 1NF has nothing to do with repeating groups or atomicity, and that 1NF could even include relvars inside of relvars (an example Joe shows 1NF preventing).