空值在多少种语言中不等于空值? [英] In how many languages is Null not equal to anything not even Null?

问题描述

在多少种语言中，Null等于甚至不等于Null?

In how many languages is Null not equal to anything not even Null?

推荐答案

在SQL中(作为逻辑语言)是这种方式，因为null表示未知/未定义.

It's this way in SQL (as a logic language) because null means unknown/undefined.

但是，在编程语言(例如C ++或C#)中，空指针/引用是具有特定含义的特定值-没什么.

However, in programming languages (like say, C++ or C#), a null pointer/reference is a specific value with a specific meaning -- nothing.

两个虚无是等价的，但是两个未知是不对的.混淆是由于两个概念使用相同的名称(空).

Two nothings are equivilent, but two unknowns are not. The confusion comes from the fact that the same name (null) is used for both concepts.

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