Unexpected Result for an Index

Summary

Wrong result with index lookup on a DECIMAL integer-scale column: predicates with non-zero fractional constants return rows after index creation, while the same predicates correctly return empty results without index.

Product / Version

• MariaDB Server `12.3.1-MariaDB`

Environment

• OS: ubuntu22.04

Steps to Reproduce

```sql
CREATE DATABASE IF NOT EXISTS logic_hunt;
USE logic_hunt;

DROP TABLE IF EXISTS d0;
CREATE TABLE d0(c DECIMAL(10,0));
INSERT INTO d0 VALUES (1),(2);

– no index: empty result (correct)
SELECT COUNT( * ) FROM d0 WHERE c = 1.2;
SELECT COUNT( * ) FROM d0 WHERE c IN (1.2);

CREATE INDEX i0 ON d0(c);

– after index: wrong result
SELECT COUNT( * ) FROM d0 WHERE c = 1.2;
SELECT COUNT( * ) FROM d0 WHERE c IN (1.2);
```

Expected Result

• `c = 1.2` and `c IN (1.2)` should both return `0` rows, regardless of index presence.
• Since `c` is `DECIMAL(10,0)`, a constant with a non-zero fractional part should not match any row under equality semantics.

Actual Result

• Before creating index `i0`:
• `SELECT COUNT( * ) FROM d0 WHERE c = 1.2;` -> `0`
• `SELECT COUNT( * ) FROM d0 WHERE c IN (1.2);` -> `0`
• After creating index `i0`:
• `SELECT COUNT( * ) FROM d0 WHERE c = 1.2;` -> `1` (wrong)
• `SELECT COUNT( * ) FROM d0 WHERE c IN (1.2);` -> `1` (wrong)