Subject Re: [firebird-support] seems bug : Field accepts NULL Values (empty string) even if it is defined with not null constraints ??
Author Jonathan Neve
Martijn Tonies wrote:

>>>You're answering your own question: '' (empty string) is NOT NULL.
>>>NULL is NULL (empty). An empty string is a value. NULL is a state,
>>>so is "NOT NULL".
>>IMHO, this unique feature could nearly be considered a bug...
>A bug? Why? NULL is NOT an empty string. An empty string
>is a value, NULL is a state.
>A column can have two states:
>A string column can have all sorts of values, ranging from an
>empty string to pretty much anything you can put into it.
Yes, yes, I know. I understand this, but you must admit that in
practice, an empty string, is really nothing. 0 is a value, and
therefore it makes sense that there would be a distinction between 0 and
null. However, '' can hardly be considered a value. What's the
difference between not putting anything in a column, and putting nothing
in it? :-)

The main thing is that it leads to much confusion, and that I can't
think of any situation where this subtle distinction would be useful. In
fact, if you look at TField.AsString (in Delphi), it returns '' if the
field is null. That's because Delphi doesn't have this subtle
distinction (of course). In practice, why make this distinction?

0 is a value, and visually, 0 is represented by a visible character.
There's a difference between saying that a certain price is 0 for
instance, and saying that we don't know the price. But what difference
could there ever be between '' and null, in practice?

Jonathan Neve.

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