Add CASEFOLD() function.

Jeff Davis <pgsql@j-davis.com>

From: Jeff Davis <pgsql@j-davis.com>

To: pgsql-hackers@postgresql.org

Date: 2024-12-12T09:00:15Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Fix PDF doc build.
- d2ca16bb509c 18.0 landed
Add SQL function CASEFOLD().
- bfc5992069cf 18.0 landed
Add support for Unicode case folding.
- 4e7f62bc386a 18.0 landed

Attachments

v1-0001-Refactor-case-mapping-into-provider-specific-file.patch (text/x-patch) patch v1-0001
v1-0002-Add-support-for-Unicode-case-folding.patch (text/x-patch) patch v1-0002
v1-0003-Add-SQL-function-FOLDCASE.patch (text/x-patch) patch v1-0003

Unicode case folding is a way to convert a string to a canonical case
for the purpose of case-insensitive matching.

Users have long used LOWER() for that purpose, but there are a few edge
case problems:

* Some characters have more than two cased forms, such as "Σ" (U+03A3),
which can be lowercased as "σ" (U+03C3) or "ς" (U+03C2). The CASEFOLD()
function converts all cased forms of the character to "σ".

* The character "İ" (U+0130, capital I with dot) is lowercased to "i",
which can be a problem in locales that don't expect that.

* If new lower case characters are added to Unicode, the results of
LOWER() may change.

The CASEFOLD() function solves these problems.

Patch attached.


-- 
Jeff Davis
PostgreSQL Contributor Team - AWS