Tom Lane wrote:
Darren Duncan <dar...@darrenduncan.net> writes:
I believe that the best general solution here is for every ordered base type to
just have a single total order, which is always used with that type in any
generic order-sensitive operation, including any ranges defined over it, or any
ORDER BY or any <,>,etc.
We've spent years and blood on making sure that Postgres could support
multiple orderings for any datatype; and there are plenty of natural
examples for the usefulness of that. So I'm not at all impressed by
any line of reasoning that starts out by baldly throwing that away.
I'm not saying that you can't use multiple orderings with a data type. I'm just
saying that the type only has *at most* one (possibly none) *native* ordering,
which is what is used when you do something ordered-sensitive with the type,
such as have a range.
To be specific, if the type system supports a concept like Perl 6 roles (or
other languages have similar concepts) where types can declare themselves
members of a union type such as "Ordered", then types of that union would have
the native ordering and other types wouldn't and then generic range operators
could be declared over ANYORDERED or such.
When we want to have some other "native" ordering for an existing type, such as
when we want to use a different text collation, we do this by creating a *new
base type*,
Nope. This has all sorts of problems that you're conveniently ignoring,
beginning with the need to duplicate all of the infrastructure for the
type (such as non-ordering-related operators), and then moving into
difficulties arising from added ambiguity as to which operator is meant.
Well a related solution is to have exactly 1 text wrapper type which has 2
attributes, one being the text value and the other being the collation name.
Then you just have 1 type that does the job instead a separate one per
collation. But to keep the semantics, the collation name is part of the
identity of the type. For example:
CREATE TYPE collated_text AS (t text, c collation);
The key point I'm trying to support is that collation issues are firmly attached
to the text type, not the range type.
Anyway, if a better solution can be arrived at for the problem at hand, then
good for the team; meanwhile, what I've proposed is the best one I can think of.
-- Darren Duncan
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
