The following bug has been logged on the website:
Bug reference: 19641
Logged by: Suyang Zhong
Email address: syzhong16@gmail.com
PostgreSQL version: 19beta3
Operating system: Ubuntu 22.04
Description:
Hi,
Consider the following test case:
CREATE COLLATION nd (provider = icu, locale = 'und-u-ks-level2',
deterministic = false);
CREATE TABLE t0(c1 text);
INSERT INTO t0 VALUES ('ALPHA');
CREATE INDEX ON t0 USING spgist (c1 COLLATE nd);
SELECT c1, c1 COLLATE nd = 'alpha' AS p FROM t0;
-- ALPHA | t
SET enable_seqscan = off;
SELECT count(*) FROM t0 WHERE c1 COLLATE nd = 'alpha';
-- Expected: 1, Actual: 0
RESET enable_seqscan;
SELECT count(*) FROM t0 WHERE c1 COLLATE nd = 'alpha';
-- 1
The predicate evaluates to true for the row, so filtering on the same
predicate should return it.
The original test case, where the planner chooses the index by itself:
CREATE TABLE t1(c1 text);
INSERT INTO t1
SELECT CASE WHEN i % 3 = 0 THEN 'alpha'
WHEN i % 3 = 1 THEN 'ALPHA'
ELSE 'beta' END
FROM generate_series(1, 340) AS i;
CREATE INDEX ON t1 USING spgist (c1 COLLATE nd);
SELECT count(*) FROM t1 WHERE c1 COLLATE nd = 'alpha';
-- Expected: 227, Actual: 113
With the v2 patch from #19633 applied, this case is still unchanged.
Reproduced on 20devel, 19beta3 and 18.6.
