Re: NULLS and string concatenation

On Fri, 19 Nov 2004 15:01:42 -0500, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Don Drake <dondrake(at)gmail(dot)com> writes:
> > This is still strange to me. In Oracle, the same query would not
> > replace the *entire* string with a NULL, it treats the NULL as a no
> > value.
>
> Oracle is a bit, um, standards-challenged. They fail to make a
> distinction between an empty string and a NULL, but such a distinction
> is both logically necessary and required by the SQL standard.
>
> > I can't find in the documentation where string concatenation of any
> > string and NULL is NULL.
>
> SQL92 section 6.13 <string value expression>, General Rule 2a:
>
> a) If either S1 or S2 is the null value, then the result of the
> <concatenation> is the null value.
>
> regards, tom lane
>

Thanks for the responses. I now have a better appreciation for the
SQL standard and PostgreSQL.

-Don