Re: So what's null then if it's not nothing?

From: <s.j.lagoe_at_googlemail.com>
Date: 10 Dec 2005 18:12:26 -0800
Message-ID: <1134267146.767667.96760@g43g2000cwa.googlegroups.com>

Hello, I have 1 question about the 3VL that hopefully someone can answer. With data that we cannot avoid is missing we may have a true/false column that can have nulls in it which gives us a 3VL so that:

((column_1=T) && (column_2=T)) = T
((column_1=T) && (column_2=F)) = F
((column_1=F) && (column_2=F)) = F
((column_1=T) && (column_2=?)) = ?
((column_1=F) && (column_2=?)) = ?
((column_1=?) && (column_2=?)) = ?

Now, I read in the thread that for this to be a sensible logic we have ?=?. Ok, but that means that an unknown equals another unknown. That does not seem to make sense because by saying ? we at the start said that we dont know values... so how can we compare them at all? thank you, Sigmund. Received on Sat Dec 10 2005 - 20:12:26 CST