Mauro Bertoli wrote:
>Hi, I've a problem creating a table. My Sql
>instruction is:
>
>CREATE TABLE questiontypes (
> id integer NOT NULL,
> flags integer,
> label text,
> UNIQUE (id,flags)
>);
>
>Is it ok?? I must have 'flags' like to NULL... but
>'id' is NOT NULL...
>Now if I insert a row:
>
>INSERT INTO questiontypes (id,flags,label) values
>(2,null,'a');
>
>and re-insert it... I can!!!! Now there are two
>identical row, and UNIQUE??
>I think postgres must occur an error? Is it Ok?
>
Hi Mauro,
yes, this is ok,
because NULL is not equal to NULL.
(In other words, every NULL is a Unique NULL).
Every comparison to NULL returns NULL.
Regards,
Dani