agora inbox for pgsql-bugs@postgresql.org  

help / color / mirror / Atom feed

From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: 303677365@qq.com
Subject: BUG #19681: ILIKE rejected on nondeterministic collations while LIKE works
Date: Tue, 08 Sep 2026 07:05:18 +0000
Message-ID: <19681-074ed6100d92cc5b@postgresql.org> (raw)

The following bug has been logged on the website:

Bug reference:      19681
Logged by:          chunling qin
Email address:      303677365@qq.com
PostgreSQL version: 18.6
Operating system:   x86_64
Description:        

On a column with a nondeterministic (case-insensitive) collation, the
pattern-matching operators split into two contradictory groups:
CREATE COLLATION ci (provider = icu, locale = 'und-u-ks-level2',
deterministic = false);
CREATE TABLE ndt(b text COLLATE ci);
INSERT INTO ndt VALUES ('a'),('A'),('str'),('STR'),('Hello');

Group 1 — silently supported (documented for LIKE):
SELECT count(*) FROM ndt WHERE b LIKE 's%';          -- 2  (matches 'str'
and 'STR')
SELECT count(*) FROM ndt WHERE b LIKE 'str';         -- 2
SELECT count(*) FROM ndt WHERE b IN ('str');          -- 2
SELECT count(*) FROM ndt WHERE b = 'str';             -- 1
SELECT count(*) FROM ndt WHERE upper(b) LIKE 'S%';    -- 2  (upper+LIKE:
ILIKE's definition!)
SELECT b LIKE 'str' COLLATE ci FROM ndt WHERE b = 'STR';  -- true
(documented example form)

Group 2 — rejected with an error:
SELECT count(*) FROM ndt WHERE b ILIKE 's%';          -- ERROR:
nondeterministic collations are not supported for ILIKE
SELECT b ILIKE 'str' COLLATE ci FROM ndt;            -- ERROR: same
SELECT count(*) FROM ndt WHERE b ~ '^s';              -- ERROR:
nondeterministic collations are not supported for regular expressions
SELECT count(*) FROM ndt WHERE b SIMILAR TO 's%';     -- ERROR: same

The documentation (func-matching.sgml) states that LIKE supports
nondeterministic collations and that SIMILAR TO / POSIX regex do not — but
says nothing about ILIKE. Meanwhile ILIKE's documented definition is exactly
"matches LIKE, but case-insensitively" (implemented as case folding + LIKE),
and that folding path works fine on the same column (upper(b) LIKE 'S%'
returns 2 rows). The citext extension — the other case-insensitive subsystem
— accepts ILIKE without error on its columns, making the ND-collation
rejection of the same operator even more inconsistent.

Message-ID: <19681-074ed6100d92cc5b@postgresql.org>
Permalink:  ../19681-074ed6100d92cc5b@postgresql.org/
Also on:    postgresql.org/message-id/19681-074ed6100d92cc5b@postgresql.org

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-bugs@postgresql.org
  Cc: noreply@postgresql.org, pgsql-bugs@lists.postgresql.org, 303677365@qq.com
  Subject: Re: BUG #19681: ILIKE rejected on nondeterministic collations while LIKE works
  In-Reply-To: <19681-074ed6100d92cc5b@postgresql.org>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox