runtime error: index out of range [7] with length 4

[DerZc]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

The following test case triggers a runtime error:

CREATE TABLE t1(c0 FLOAT UNSIGNED ZEROFILL , PRIMARY KEY(c0));
INSERT INTO t1(c0) VALUES (0.3);
SET @a = 602065819;
PREPARE prepare_query FROM 'SELECT IF(?, t1.c0, t1.c0) FROM t1 WHERE t1.c0 GROUP BY true';
EXECUTE prepare_query USING @a; -- runtime error: index out of range [7] with length 4
DEALLOCATE PREPARE prepare_query; 

2. What did you expect to see? (Required)

No error.

3. What did you see instead (Required)

runtime error: index out of range [7] with length 4

4. What is your TiDB version? (Required)

tidb_version()
Release Version: v9.0.0-beta.2.pre-855-gbc50e0d3e2\nEdition: Community\nGit Commit Hash: bc50e0d\nGit Branch: master\nUTC Build Time: 2025-12-05 12:40:26\nGoVersion: go1.23.12\nRace Enabled: false\nCheck Table Before Drop: false\nStore: unistore\nKernel Type: Classic