Query result may be wrong when use like to do index range scan on PAD SPACE column

[time-and-fate]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a varchar(20) collate utf8mb4_bin, index ia(a));
insert into t value('测试'),('测试  ');
select *,length(a) from t where a like '测试 %';
select *,length(a) from t where a like '测试';

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

From mysql:

> select *,length(a) from t where a like '测试 %';
+----------+-----------+
| a        | length(a) |
+----------+-----------+
| 测试     |         8 |
+----------+-----------+

> select *,length(a) from t where a like '测试';
+--------+-----------+
| a      | length(a) |
+--------+-----------+
| 测试   |         6 |
+--------+-----------+

3. What did you see instead (Required)

> select *,length(a) from t use index () where a like '测试 %';
+----------+-----------+
| a        | length(a) |
+----------+-----------+
| 测试     |         8 |
+----------+-----------+

> select *,length(a) from t use index (ia) where a like '测试 %';
+----------+-----------+
| a        | length(a) |
+----------+-----------+
| 测试     |         6 |
| 测试     |         8 |
+----------+-----------+

> select *,length(a) from t use index () where a like '测试';
+--------+-----------+
| a      | length(a) |
+--------+-----------+
| 测试   |         6 |
+--------+-----------+

> select *,length(a) from t use index (ia) where a like '测试';
+----------+-----------+
| a        | length(a) |
+----------+-----------+
| 测试     |         6 |
| 测试     |         8 |
+----------+-----------+

4. What is your TiDB version? (Required)

From v6.0.0 to latest master