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Comment by grahamlee | Hacker News Reader

Exactly this. SQL is based on the relational algebra and that's well-defined, NULL along with other features of SQL work in an entirely regular and predictable way. The only time it's weird is when a developer decides that it should work the way Javascript (or whatever) NULLs work because that's the last time they saw the same word used in a programming language, in which case it's the assumption that's weird.

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That's not the only time it is weird. There's even a whole book by one of the pioneers of the relational DB model, Date's "Database Technology: Nulls Considered Harmful" [1], covering many of the ways it is weird.

[1] https://www.amazon.com/Database-Technology-Nulls-Considered-...

The part that’s weird with nulls is that it’s a trinary logic stuffed into a boolean algebra. The use of x = NULL instead of x IS NULL is pretty much always a mistake.

More importantly, x = value instead of (x = value and x IS NOT NULL) is almost always a mistake, and a stupidly subtle one at that. And for this curse, we get… nothing particularly useful from these semantics.

Also the x != NULL case is completely cursed

> The part that’s weird with nulls is that it’s a trinary logic stuffed into a boolean algebra.

It's a three-valued logic (though not trinary, which would use a base-3 number system) in a three-valued algebra: specifically, the relational algebra. The outcome of a logical test has three values: true, false, or NULL; this is distinct from Boole's algebra where outcomes have a continuous value between 0 and 1 inclusive.

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