charset: incorrect result when querying in-txn updates when new collation is enabled

[bb7133]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE test.`t` (
  `a` bigint(20) primary key,
  `b` varchar(50) COLLATE utf8_general_ci DEFAULT NULL,
  `c` int,
  `d` int,
    UNIQUE KEY `idx_bc` (`b`, `c`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

INSERT INTO t VALUES (1, 'A', 10, 1);
INSERT INTO t VALUES (2, 'B', 20, 1);

BEGIN;
SELECT * FROM t WHERE c = 10;
UPDATE t SET c = 5 WHERE c = 10;
SELECT * FROM t FORCE INDEX(idx_bc) WHERE b = 'A';
ROLLBACK;

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

tidb> SELECT * FROM t FORCE INDEX(idx_bc) WHERE b = 'A';
+---+------+------+------+
| a | b    | c    | d    |
+---+------+------+------+
| 1 | A    |    5 |    1 |
+---+------+------+------+
1 row in set (0.01 sec)

3. What did you see instead (Required)

tidb> SELECT * FROM t FORCE INDEX(idx_bc) WHERE b = 'A';
Empty set (0.00 sec)

4. Affected version (Required)

v4.0.0 - v4.0.2

5. Root Cause Analysis

To be filled

[bb7133]

Close this issue since it is fixed by #18703