The Database Design Resource Center

NULLs have meaning, IMHO

by Tomislav Bijelonjic
(Zagreb, Croatia)

I'll give you just one example where NULL _IS_ a value (and has defined meaning):

Let's say you have a table "Order"
with columns: OrderID (int), CustomerID (int), OrderedOn (date), DeliveredOn (date)

If you allow DeliveredOn to be NULL, then you don't need another column "IsDelivered",
because if it is Null - that means it is NOT yet delivered, and you save database space,
because you WILL NEED Delivery date anyway, but you don't NEED "IsDelivered" field.

One field less - database is a little bit faster.

In computers, it is used Binary sistem (base 2), but ideal numeric base is "base e" (, which is aprox. 2,72 (almost 3!).
When being asked, someone can shortly answer: yes/no/maybe.

NULL's "uncertainty" is information for itself - "I don't know". If you say YES or NO, you would be lying.

So, NULL is mandatory, because it's information (value) is "something is missing".

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