Re: Does UCS_BASIC have the right CTYPE?

Peter Eisentraut wrote:

> > That seems to suggest the standard answer should be 'Á' regardless of
> > any COLLATE clause (though I could be misreading). I'm a bit confused
> > by that... what's the standard-compatible way to specify the locale for
> > UPPER()/LOWER()? If there is none, then it makes sense that Postgres
> > overloads the COLLATE clause for that purpose so that users can use a
> > different locale if they want.
>
> The standard doesn't have the notion of locale-dependent case conversion.

Neither does Unicode, which is why the ICU functions like u_isupper()
or u_toupper() don't take a locale argument.

With libc, isupper_l() and the other ctype functions need a locale
argument, but given a locale's value of
"language[_territory][.codeset]", in theory only the codeset part is
actually useful.

To me the question of what we should put in pg_collation.collctype
for the "ucs_basic" collation leads to another question which is:
why do we even consider collctype in the first place?

Within a database, there's only one "codeset", which corresponds
to pg_database.encoding, and there's a value in pg_database.lc_ctype
that is normally compatible with that encoding.
ISTM that UPPER(string COLLATE "whatever") should always give
the same result than UPPER(string COLLATE pg_catalog.default). And
likewise all functions that depend on character categories could
basically ignore the COLLATE specification, given that our
database-wide properties are sufficient to characterize the strings
within.

Best regards,
--
Daniel Vérité
https://postgresql.verite.pro/
Twitter: @DanielVerite