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by chris_wot
1445 days ago
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Well, if NULL is most often meant to signify an unknown value. You can't compare one unknown value with another and say they are the same. The standard is, I believe, ambiguous about NULL because it can also mean that it is an absence of data. In other words, it is "this is not yet determined" (aka a CAR table has a COLOR table, but the paint is applied as the final operation so NULL could be used as the car is not at this stage yet and the color will be chosen later). In this case, you can compare NULLs against other NULLs, because you can have two cars that are in an indeterminant state. In that case, it is useful to compare to NULL values as it means the same thing. |
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