LIKE translation is collate sensitive

[sisidra]

What happens?

Consider query:

select endpoint from logs where endpoint like '/api/%'

It translates to following PostgreSQL queries (got from SET pg_debug_show_queries = TRUE):

BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ

COPY (SELECT "endpoint" FROM "postgres"."logs" WHERE ctid BETWEEN '(0,0)'::tid AND '(1000,0)'::tid AND ("endpoint" >= '/api/' AND "endpoint" < '/api0')) TO STDOUT (FORMAT "binary");

COPY (SELECT "endpoint" FROM "postgres"."logs" WHERE ctid BETWEEN '(1000,0)'::tid AND '(4294967295,0)'::tid AND ("endpoint" >= '/api/' AND "endpoint" < '/api0')) TO STDOUT (FORMAT "binary");

COMMIT

Looks almost reasonable, only text comparison in Postgres is collate sensitive. See:

select
    '/api/something' < '/api0' COLLATE "en_US.utf8" AS collate_en_us_wrong,
    '/api/something' < '/api0' COLLATE "C" AS collate_c_correct,
    '/api/something' < '/api0' COLLATE "unicode" AS collate_unicode_correct,
    '/api/something' LIKE '/api/%' AS like_correct

Output:

collate_en_us_wrong	collate_c_correct	collate_unicode_correct	like_correct
f	t	t	t

As a result we get incorrect results - for example like '/%' yields no rows and like 'a%' yields all rows for table containing absolute paths.

To Reproduce

1. Attach to postgresql
2. Ensure default collate is "en_US.utf8"
3. Match path-like data with LIKE '/%

OS:

MacOS Sequoia

PostgreSQL Version:

PostgreSQL 17.5 (Debian 17.5-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

DuckDB Version:

v1.3.2 (Ossivalis) 0b83e5d2f6

DuckDB Client:

v1.3.2 (Ossivalis) 0b83e5d2f6

Full Name:

Mārtiņš Kalvāns

Affiliation:

NymTech

Have you tried this on the latest main branch?

• I agree

Have you tried the steps to reproduce? Do they include all relevant data and configuration? Does the issue you report still appear there?

• I agree

[sisidra]

Here is my exploration trace that might or might not help:

• PatternIsPrefix optimization translates LIKE '[^%_]*[%]+' to prefix function.
• PrefixFilter implementation creates observed filters.

I have no context nor knowledge if the fix is in this repo or duckdb, or both. Nor is solution restructuring optimizations, adding collations or anything else.

Hope it helps.