Re: Shouldn't "WHEN (OLD.* IS DISTINCT FROM NEW.*)" clause be independent from data type?

On 09/17/2015 06:32 AM, Albe Laurenz wrote:
> pinker wrote:
>> I've tried to write audit trigger which fires only when data changed, so I used "WHEN (OLD.* IS
>> DISTINCT FROM NEW.*)" clause as described in documentation
>> <http://www.postgresql.org/docs/9.4/static/sql-createtrigger.html> . Should this clause be independent
>> from data type? because an error occurs when I'm trying to modify row with point data type: ERROR:
>> could not identify an equality operator for type point
>
> I guess it is dependent on data type as it requires an equality operator,
> and type "point" doesn't have one.

To echo the OP, why is that?

http://www.postgresql.org/docs/9.4/interactive/functions-comparison.html

For non-null inputs, IS DISTINCT FROM is the same as the <> operator.

So:

test=> select '(1,2)'::point <> '(1,2)'::point;
?column?
----------
f
(1 row)

test=> select '(1,2)'::point <> '(1,3)'::point;
?column?
----------
t

test=> select '(1,2)'::point <> null;
?column?
----------

(1 row)

>
> You'd have to hand-roll a comparison in this case, probably using the
> "same as" operator "~=".

I could force it to work by casting:

test=> select '(1,2)'::point::text is distinct from '(1,2)'::point::text;
?column?
----------
f
(1 row)

test=> select '(1,2)'::point::text is distinct from '(1,3)'::point::text;
?column?
----------
t
(1 row)

test=> select '(1,2)'::point::text is distinct from null;
?column?
----------
t

>
> Yours,
> Laurenz Albe
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com