I don't understand your comment or perhaps you misread my comment or I misread yours. First of all I never said or suggested that a NULL field has "any value"; instead I said that "any value" should be ignored etc. because the field should be treated as not having a value. Second I disagree with the statement that even if I had implied that a NULL field had "any value", then every logical operation would return TRUE. Perhaps you are confusing this with a convention in mathematics which says exactly the opposite: that any statement about the elements of an empty set is TRUE.

The reason why I used so many words to say that the field should be treated as not having a value, is that apparently this simple statement is not enough. People still continue to discuss, for example, what NULL means for the value of the field (is it missing, or unknown, or what...) whereas such a discussion is totally inappropriate. Considering the mathematical background of the relational model the only interpretation of NULL that makes any sense to me is the minimalistic interpretation that there is no value. Period. Anything beyond that is too much speculation when it is done in discussing the meaning of NULL in general.