Re: PATCH: CITEXT 2.0

David E. Wheeler napsal(a):
> On Jul 7, 2008, at 12:21, David E. Wheeler wrote:
>
>> My question is: why? Shouldn't they all use the same function for
>> comparison? I'm happy to dupe this implementation for citext, but I
>> don't understand it. Should not all comparisons be executed consistently?
>
> Let me try to answer my own question by citing this comment:
>
> /*
> * Since we only care about equality or not-equality, we can avoid
> all the
> * expense of strcoll() here, and just do bitwise comparison.
> */
>
> So, the upshot is that the = and <> operators are not locale-aware, yes?
> They just do byte comparisons. Is that really the way it should be? I
> mean, could there not be strings that are equivalent but have different
> bytes?

Correct. The problem is complex. It works fine only for normalized string. But
postgres now assume that all utf8 strings are normalized.

If you need to implement < <= >= > operators you need to use strcol which take
care of locale collation.

See unicode collation algorithm http://www.unicode.org/reports/tr10/

Zdenek

--
Zdenek Kotala Sun Microsystems
Prague, Czech Republic http://sun.com/postgresql