On Thu, Sep 17, 2015 at 9:39 AM, Adrian Klaver <adrian.kla...@aklaver.com> wrote:
> 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) > > ​SELECT not ('(0,4)'::point = '(1,2)'::point) ERROR: operator does not exist: point = point If it calling it a bug gets it changed I'm game...but IS DISTINCT FROM apparently looks for an equality operator and then performs negation instead of looking for a "non-equality" operator. Since the latter doesn't really even make sense (TBH it's probably syntatic sugar transformed by the parser) I don't blame it. David J.
