[thedataslinger]

This is not true--especially when considering different SQL implementations (e.g. Oracle SQL versus Microsoft SQL). NULL and EMPTY handle the intersection of ontic versus epistemic claims.

EMPTY implies a known, 0-byte value whereas NULL can imply either an unknown value or the "unknowability" of a value (i.e. the in-existence of a value).

In practical terms, this would be like equating the statements "I don't know whether that dog has a name" (i.e. a NULL name) and "I do not know the name of that dog" (an EMPTY name). The former does not assert the existence of a proper noun to represent "that dog", whereas the latter implicitly asserts that there exists a proper noun which nominates "that dog".

[gfody]

beg pardon I wasn't aware sql actually defined empty. of the engines I'm familiar with there is no keyword for empty like what gp is asking for (and I hold my argument for why it should not be necessary). it sounds like what you're describing is a blank string and I agree with using blanks to distinguish between "has no phone number" and "we don't know their phone number" but that isn't what gp was talking about.