"NULL only has one meaning: NULL. This is roughly analogous to unknown."
From the re-published version of "Much ado about nothing, part 2" (re-published in "Database Dreaming, Vol II) :
"An outer join produces nulls because we ask the DBMS to show us data from one table even when no matching data can be found in another table. Such nulls have no meaning, no semantic content."
Personally I'd add to that : and even if it's the case that they do, that meaning is patently not "simply unknown" but rather a very clear indication of non-existence.
But I have no doubt the apologists will obviously always apologize no matter what and handwave arguments such as these away with "So what ? What's the difference." Well, it's the difference between knowing of non-existence and not knowing at all.
From the re-published version of "Much ado about nothing, part 2" (re-published in "Database Dreaming, Vol II) :
"An outer join produces nulls because we ask the DBMS to show us data from one table even when no matching data can be found in another table. Such nulls have no meaning, no semantic content."
Personally I'd add to that : and even if it's the case that they do, that meaning is patently not "simply unknown" but rather a very clear indication of non-existence.
But I have no doubt the apologists will obviously always apologize no matter what and handwave arguments such as these away with "So what ? What's the difference." Well, it's the difference between knowing of non-existence and not knowing at all.