Re: [SQL] NULL

Bruce Stephens ha scritto:

> Goran Thyni <goran@kirra.net> writes:
>
> > How about this according to SQL standard:
> >
> > CREATE TABLE x { y integer NULL };
> >
> > It suppose to mean that NULLs are explicitly allowed in
> > this field.
> > Is this required by SQL-92?
>
> No, it's not required.  This came up before with the examples from
> "The Practical SQL Handbook".  It would be nice to allow it, but there
> was some reason why to do so would be non-trivial, which I forget.
> Anyway, it's not in SQL-92.
>
> ************

Sorry, I don't understand why we need this feature. This is completely out
of standard.

What's that mean ?

-  Is it a constraint to allow only NULL values ?  (unuseful)

- If this is a default value we already have this in:
  CREATE TABLE  table1 (field1  int DEFAULT NULL);

- According with SQL-92 every column can store a NULL value by default
  unless one specify a NOT NULL constraint for the column.

José