Why doesn't SQL support “= null” instead of “is null”?

Question

I\'m not asking if it does. I know that it doesn\'t.

I\'m curious as to the reason. I\'ve read support docs such as as this one on Working With Nu

Answer 1

a. Null is not the "lack of a value"

b. Null is not "empty"

c. Null is not an "unset value"

It's all of the above and none of the above.

By technical rights, NULL is an "unknown value". However, like uninitialized pointers in C/C++, you don't really know what your pointing at. With databases, they allocate the space but do not initialize the value in that space.

So, it is an "empty" space in the sense that it's not initialized. If you set a value to NULL, the original value stays in that storage location. If it was originally an empty string (for example), it will remain that.

It's a "lack of a value" in the fact that it hasn't been set to what the database deems a valid value.

It's an "unset value" in that if the space was just allocated, the value that is there has never been set.

"Unknown" is the closest that we can truly come to knowing what to expect when we examine a NULL.

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Because of that, if we try to compare this "unknown" value, we will get a comparison that

a) may or may not be valid

b) may or may not have the result we expect

c) may or may not crash the database.

So, the DBMS systems (long ago) decided that it doesn't even make sense to use equality when it comes to NULL.

Therefore, "= null" makes no sense.