Comments on: Should you have NULL’s in your database?

By: NULL Conclusion | A Foolish Manifesto

NULL Conclusion | A Foolish Manifesto — Tue, 14 Jul 2009 06:36:44 +0000

[...] a couple perl giants I have already heard of responded to my previous post regarding NULL’s in the database. NULL means “this piece of information exists but is [...]

By: Ovid

Ovid — Mon, 13 Jul 2009 14:32:04 +0000

I’ve a blog entry about this (http://use.perl.org/~Ovid/journal/27927). Basically, NULLs can lead to queries which are logically impossible to get correct answers for. They’re rare, but I’ve hit them on larger queries and they’re a nightmare to debug.

There’s also the problem of what a NULL is supposed to represent. Is the data unknown? Is it not applicable? Is it something else entirely? I often see NULL values in a databsae where people have tried to overload the meaning of NULL and it’s done on an ad hoc basis. For example, consider a “salary” field in a database. Why would it be NULL? Are they unemployed? Are they a volunteer? Do you simply not know it? Are they hourly and therefore not salaried? A NULL value could potenitally have four different meanings.

By: ruz

ruz — Mon, 13 Jul 2009 11:14:57 +0000

You’re right, all that “NULLs must die” is about empty strings, while I think that empty string should be treated as NULL. Oracle does this.

By: Matt S Trout

Matt S Trout — Sun, 12 Jul 2009 18:26:00 +0000

NULL means “this piece of information exists but is unknown to us”. Follow this simple rule when deciding whether to allow things to be NULL or not and you’re basically sorted – and the standard SQL logic will suddenly work with you rather than against.

Until you do a LEFT JOIN and discover that it uses NULLs for “doesn’t exist” in there … but anyway …