Inconsistent evaluation of NULLIF(ROUND(VAR_SAMP(...)), const) <= value between MySQL and PostgreSQL/DuckDB causes different query results

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
``` SQL
-- SCHEMA
CREATE TABLE users (
id INT,
username VARCHAR(100),
email VARCHAR(255),
age INT,
status VARCHAR(20),
created_at TIMESTAMP NULL,
score DOUBLE
);

CREATE TABLE posts (
id INT,
user_id INT,
title VARCHAR(255),
content VARCHAR(1000),
views INT,
likes INT,
created_at TIMESTAMP NULL,
rating DOUBLE
);

INSERT INTO users VALUES
(1, 'alice', 'alice@test.com', 20, 'active', '2022-01-01 10:00:00', 88.5),
(2, 'bob', 'bob@test.com', 30, 'active', '2022-01-02 11:00:00', 92.3),
(3, 'carol', NULL, NULL, 'banned','2022-01-03 12:00:00', NULL),
(4, 'dave', 'dave@test.com', 45, 'active', '2022-01-04 13:00:00', 65.2),
(5, NULL, 'null@test.com', 18, 'inactive','2022-01-05 14:00:00', 70.0);

INSERT INTO posts VALUES
(1, 1, 'Hello World', 'First post', 100, 10, '2022-01-10 10:00:00', 4.5),
(2, 1, 'Another Post', NULL, 150, 20, '2022-01-11 11:00:00', 3.0),
(3, 2, 'Bob Post', 'Content', NULL, 5, '2022-01-12 12:00:00', NULL),
(4, 3, NULL, 'Empty', 50, 2, '2022-01-13 13:00:00', 5.0),
(5, 4, 'Last Post', 'Last', 300, 30,'2022-01-14 14:00:00', 4.9);

-- TRIGGER SQL
SELECT COUNT(*)
FROM users AS ref_0
WHERE NULLIF(
ROUND((SELECT VAR_SAMP(id) FROM posts)),
86.82
) <= 2;

-- Expected result: 0, Actual Result(TiDB): 5
```

### 2. What did you expect to see? (Required)
In both PostgreSQL and DuckDB, the condition evaluates in a way that results in no rows matching, which is the expected and standard SQL behavior.
### 3. What did you see instead (Required)
In MySQL, the following query returns 5 rows, while results in no rows matching is the expected and standard SQL behavior.
### 4. What is your TiDB version? (Required)
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version() |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v7.5.1
Edition: Community
Git Commit Hash: 7d16cc79e81bbf573124df3fd9351c26963f3e70
Git Branch: heads/refs/tags/v7.5.1
UTC Build Time: 2024-02-27 14:28:32
GoVersion: go1.21.6
Race Enabled: false
Check Table Before Drop: false
Store: unistore |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+