On 09/17/2015 07:34 AM, Tom Lane wrote:
> Adrian Klaver <adrian.klaver@aklaver.com> writes:
>> On 09/17/2015 06:54 AM, Tom Lane wrote:
>>> Well, that's true: the parser actually looks up the operator named "<>"
>>> for the given data types, and IS DISTINCT FROM is just a prefilter on
>>> that to do the right thing with nulls. So because type point has an
>>> operator that's physically named "<>", that case works.
>
>> If you use '<>' explicitly, otherwise:
>> test=> select '(1,2)'::point is distinct from '(1,3)'::point;
>> ERROR: operator does not exist: point = point
>
> Ah, sorry, actually what IS [NOT] DISTINCT FROM looks up is the "="
> operator.
So the docs should be changed?
As they stand now:
http://www.postgresql.org/docs/9.4/interactive/functions-comparison.html
"For non-null inputs, IS DISTINCT FROM is the same as the <> operator. "
That did not indicate to me the '=' was important to IS DISTINCT ON.
Then again I may need more attention from the clue stick:)
The core point remains, though, that this is a name-based
> lookup rather than an opclass-based one. I'd like to get us moved
> over to using opclass-based lookups for all cases where the system
> currently assumes that operators named "=" or "<>" necessarily behave
> in a particular way. However, that would leave point and some of the
> other weirder datatypes even further out in the cold than they are now.
>
> regards, tom lane
>
--
Adrian Klaver
adrian.klaver@aklaver.com