Joshua Tolley <eggyknap@gmail.com> writes:
> On Thu, Jul 23, 2009 at 06:46:25PM -0700, David E. Wheeler
>> Yes, but given that the standard says that `ROW(1, NULL)` is NULL, then I
>> would expect it to be NOT DISTINCT from `ROW(2, NULL)`.
> Wait, didn't we decide upthread that the standard said ROW(1, NULL) isn't
> NULL?
David misspoke in the quoted statement, as I believe he figured out soon
thereafter. For that row value, neither IS NULL nor IS NOT NULL will
return true. The spec defines them in such a way that they are not inverses
for row values.
SQL2008 points out:
NOTE 219 - For all R, "R IS NOT NULL" has the same result as "NOT R IS NULL" if and only if R is
ofdegree 1. Table 14, "<null predicate> semantics", specifies this behavior.
That table looks like this:
R IS R IS NOT NOT R IS NOT R IS NOT
_Expression_______NULL____NULL__________NULL__________NULL_________
| degree 1: null | true_ | false_ | false_ | true_ | | | |
| | | | degree 1: not | false_| true_ | true_ | false_ | null
| degree > 1: | true_ | false_ | false_ | true_ | | all null | |
| | | | | | | | | | degree
>1: | false_| false_ | true_ | true_ | | some null | | | |
| | | | | | | | degree > 1: |
false_|true_ | true_ | false_ |
|_none_null______|_______|_____________|____________|______________|
regards, tom lane
