Re: Per-column collation, proof of concept

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> Well, the comparison function varstr_cmp() contains this comment:

> /*
> * In some locales strcoll() can claim that nonidentical strings are
> * equal. Believing that would be bad news for a number of reasons,
> * so we follow Perl's lead and sort "equal" strings according to
> * strcmp().
> */

> This might not be strictly necessary, seeing that citext obviously
> doesn't work that way, but resolving this is really an orthogonal issue.

The problem with not doing that is it breaks hashing --- hash joins and
hash aggregation being the real pain points.

citext works around this in a rather klugy fashion by decreeing that two
strings are equal iff their str_tolower() conversions are bitwise equal.
So it can hash the str_tolower() representation. But that's kinda slow
and it fails in the general case anyhow, I think.

regards, tom lane