BITMAP Index Scan Returns Wrong Results for FLOAT Column with BETWEEN Operator

1. Minimal reproduce step

DROP DATABASE IF EXISTS bug_repro;
CREATE DATABASE bug_repro;
USE bug_repro;
CREATE TABLE t (c0 INT, c2 FLOAT) ENGINE=InnoDB;
INSERT INTO t VALUES (1, 3.0E38), (2, 3.4028235E38), (3, 1.5), (4, NULL), (5, 2.0E38);
CREATE INDEX idx_c2 ON t (c2);
ANALYZE TABLE t;

-- [CORRECT] Full table scan (IGNORE INDEX)
SELECT '[CORRECT]' AS plan, COUNT(*) FROM t IGNORE INDEX(idx_c2)
 WHERE c2 BETWEEN 0 AND 3.4028235E38 OR c2 IS NULL;

-- [BUG] Index scan (FORCE INDEX)
SELECT '[BUG]   ' AS plan, COUNT(*) FROM t FORCE INDEX(idx_c2)
 WHERE c2 BETWEEN 0 AND 3.4028235E38 OR c2 IS NULL;

2. What did you expect to see?

Both queries should return 5, since all 5 rows satisfy the condition (c2 BETWEEN 0 AND 3.4028235E38 OR c2 IS NULL):

plan        COUNT(*)
[CORRECT]   5
[BUG]       5

3. What did you see instead (Required)

The FORCE INDEX query returns only 1 (only the NULL row), losing all 4 non-NULL FLOAT rows:

plan        COUNT(*)
[CORRECT]   5
[BUG]       1

Further diagnosis:

Breaking down the BETWEEN into its logical equivalent c2 >= 0 AND c2 <= 3.4028235E38 via FORCE INDEX returns the correct result (4 rows, NULL excluded by AND semantics):

-- [OK] Equivalent AND condition via FORCE INDEX — correct
SELECT COUNT(*) FROM t FORCE INDEX(idx_c2)
 WHERE c2 >= 0 AND c2 <= 3.4028235E38 OR c2 IS NULL;
-- Returns: 5

This confirms the bug is specific to the SQL BETWEEN operator when used via index scan on FLOAT columns. The >= AND <= equivalent works correctly, but BETWEEN does not.

Additional verification:

• c2 >= 0 OR c2 IS NULL via FORCE INDEX → 5 ✔
• c2 <= 3.4028235E38 OR c2 IS NULL via FORCE INDEX → 5 ✔
• c2 >= 0 AND c2 <= 3.4028235E38 via FORCE INDEX → 4 ✔ (AND excludes NULL)
• c2 BETWEEN 0 AND 3.4028235E38 via FORCE INDEX → 0 ！！！WRONG

The BETWEEN operator on FLOAT columns is incorrectly transformed into a range scan condition by the BITMAP index access path, causing the upper bound to be lost. INT columns are not affected.

4. What is your PolarDB-X version?

VERSION(): 5.6.29-PXC-5.4.19-20250825

Docker image: polardbx/polardb-x:v2.4.2_5.4.19

Start by running the supplied SQL reproduction against the stated PolarDB-X version, comparing the full-table and FORCE INDEX plans. Trace the BITMAP index access path for FLOAT BETWEEN predicates and add a regression test covering the upper bound and NULL condition. Done means both queries return 5 and the standalone BETWEEN returns 4 non-NULL rows.