Обсуждение: ERROR: could not identify an equality operator for type box

Hi there,

create table qq (b box);
CREATE TABLE
select count(*), b from qq group by b;
ERROR:  could not identify an equality operator for type box
LINE 1: select count(*), b from qq group by b;

but following select works fine
 select ' (43.6038,48.8664536),(1.3620777,1.44327)'::box = ' (43.6038,48.8664536),(1.3620777,1.44327)'::box; ?column? 
---------- t
(1 row)                        ^
What does it means ?
    Regards,        Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

Ok, casting to ::text solves the problem, but still I think we 
need to fix it in the right way

Oleg
On Sat, 4 Dec 2010, Oleg Bartunov wrote:

> Hi there,
>
> create table qq (b box);
> CREATE TABLE
> select count(*), b from qq group by b;
> ERROR:  could not identify an equality operator for type box
> LINE 1: select count(*), b from qq group by b;
>
> but following select works fine
>
> select ' (43.6038,48.8664536),(1.3620777,1.44327)'::box = ' 
> (43.6038,48.8664536),(1.3620777,1.44327)'::box;
> ?column? ----------
> t
> (1 row)
>                        ^
> What does it means ?
>
>     Regards,
>         Oleg
> _____________________________________________________________
> Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
> Sternberg Astronomical Institute, Moscow University, Russia
> Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
> phone: +007(495)939-16-83, +007(495)939-23-83
>
>
    Regards,        Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

On 03.12.2010 23:53, Oleg Bartunov wrote:
> create table qq (b box);
> CREATE TABLE
> select count(*), b from qq group by b;
> ERROR: could not identify an equality operator for type box
> LINE 1: select count(*), b from qq group by b;
>
> but following select works fine
>
> select ' (43.6038,48.8664536),(1.3620777,1.44327)'::box = '
> (43.6038,48.8664536),(1.3620777,1.44327)'::box;
> ?column? ----------
> t
> (1 row)
> ^
> What does it means ?

GROUP BY requires b-tree sort operators. Although there is a '=' 
operator for box, there is no b-tree opclass.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> On 03.12.2010 23:53, Oleg Bartunov wrote:
>> create table qq (b box);
>> CREATE TABLE
>> select count(*), b from qq group by b;
>> ERROR: could not identify an equality operator for type box
>> What does it means ?

> GROUP BY requires b-tree sort operators. Although there is a '=' 
> operator for box, there is no b-tree opclass.

A hash opclass would do too, as of recent releases ... but box hasn't
got one of those either.

There are some semantic issues involved here, notably that box_eq is
actually equality-of-areas, and that both it and box_same use fuzzy
equality which does not work well with either hash or sort-based
semantics.  So you'd need to look at redefining the operator behavior
before you could get far.
        regards, tom lane