Jaime Casanova wrote:
> suppose we have something like this:
>
> upd_views=# create table tabla1 (col1 point);
[...]
> then, this select will give an error:
>
> upd_views=# select col1, count(*) from tabla1 group by col1;
> ERROR: could not identify an ordering operator for type point
> HINT: Use an explicit ordering operator or modify the query.
> upd_views=#
>
> i guess this is related to:
> http://archives.postgresql.org/pgsql-hackers/2003-08/msg00809.php
>
> so, what happened with this idea? there is another way to automagicaly
> identify an "equality operator" for datatypes like 'point'?
I don't think that there is a connection to the message you quote.
In order to (efficiently) process a GROUP BY clause, you need a
total ordering on the data type that you group by, i.e. an ordering
such that for any two data x and y you have either x < y or x > x
or x = y.
There is no reasonable total ordering on the real plain, so you will
have to roll your own. How about:
select point(col1[0], col1[1]), count(*) from tabla1 group by col1[0],
col1[1];
Yours,
Laurenz Albe
