The difference analysis of null,empty,nothing in ASP-application skills

In this paper, we introduce the sources and methods of null,empty,nothing of these kinds of null values in ASP.

Dim A
Dim B as String
Dim C as Integer
Dim D as Object

A is equal to Empty because the "unshaped variable" that has not yet been initialized equals Empty. However, if you detect a = "" or a = 0, you can also get a true value.
B equals "" because the unfixed length "string" that has not been initialized is equal to "". But please note b <> Null.
C equals 0, is this still a problem?
D equals Nothing, "object variables" that have not yet been set are equal to none, but do not use d = anything, but use D is nothing to determine if D equals anything, because the symbol that determines whether equality is not =.

The most confusing place is the Null Word, see the following statement:
Print X = Null
Print X <> Null
The result is output null (not true or false), because any expression that is null is equal to NULL, and in fact it is not possible to determine whether a data is null or not:
If X = null Then ' will always get null
and to use:
If IsNull (X) Then

Which data is equal to NULL? In addition to having a null expression, a data field (in the database) that does not enter any data is equal to NULL. That is, you can understand that null is the empty field that is read in the data.