Re: [HACKERS] Creating a VIEW with a POINT column

Tom Lane wrote:

=?UTF-8?B?SmFuIFVyYmHFhHNraQ==?= <j.urbanski@students.mimuw.edu.pl> writes:   

All three try to sort the table first, and as there's no comparision  operator for the POINT datatype, they fail. Which seems to be wrong - if  there is no comparision operator, you still can do DISTINCT, only less  efficiently.     

 Type point has no btree opclass, no hash opclass, and not even an operator named "=" (it looks like the functionality is named ~= for some odd reason).  I'd be interested to hear either a proposal of a principled way to define DISTINCT, or a way to implement it that was better than comparing every element to every other element...   

I agree - a byte-wise comparison of the internal encoding might be inadequate (compare "0.0e+1" to "0.0e+2" is "not equal" for instance?). If the poster is referring to a translation to string before comparing, this could face similar issue. What if it's not a "point" but a "fraction" - does "2/4" = "1/2"? With an operator implementing "=", making any assumption may be making the wrong assumption, and I really like that PostgreSQL will refuse to do things rather than silently continue to do what may be the wrong thing (MySQL silent truncation when assigning into a varchar(8) for example).

The problem here seems to that "point" should have an equality operator?

Cheers,
mark

--  Mark Mielke <mark@mielke.cc>