Re: SQL/JSON path: collation for comparisons, minor typos in docs

On Wed, Aug 7, 2019 at 4:11 PM Alexander Korotkov
<a(dot)korotkov(at)postgrespro(dot)ru> wrote:
> On Wed, Aug 7, 2019 at 2:25 PM Markus Winand <markus(dot)winand(at)winand(dot)at> wrote:
> > I was playing around with JSON path quite a bit and might have found one case where the current implementation doesn’t follow the standard.
> >
> > The functionality in question are the comparison operators except ==. They use the database default collation rather then the standard-mandated "Unicode codepoint collation” (SQL-2:2016 9.39 General Rule 12 c iii 2 D, last sentence in first paragraph).
>
> Thank you for pointing! Nikita is about to write a patch fixing that.

Please, see the attached patch.

Our idea is to not sacrifice "==" operator performance for standard
conformance. So, "==" remains per-byte comparison. For consistency
in other operators we compare code points first, then do per-byte
comparison. In some edge cases, when same Unicode codepoints have
different binary representations in database encoding, this behavior
diverges standard. In future we can implement strict standard
conformance by normalization of input JSON strings.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company