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The problem is that in practice in a database NULL is a placeholder for a missing value, not an unknown value.
by cm2187 2y ago
The problem is that in practice in a database NULL is a placeholder for a missing value, not an unknown value.
- bballer 2y agoAnd to further apply semantics to this just to be snide, the value is only "missing" if it could possibly ever be defined for that tuple. There are cases where you expect the value to be "missing", and it not being "missing" would be considered a data integrity issue. Fun.
- cm2187 2y agoYes I should have rather written “an absence of data”. But still not “unknown”.
- SoftTalker 2y agoBest way to think of NULL is "no value." Not "unknown value," as that implies that it is a value you just don't know what it is. Not "missing" value as that even the notion of a value being "missing" tells you something. NULL is no value. It's like a black hole, it consumes anything it touches. Any expression involving a NULL term becomes NULL.