Don Drake <dondrake@gmail.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