Wrong result of LEAST function in TiDB with MySQL

[curry-oss]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

DROP TABLE IF EXISTS t0;
CREATE TABLE IF NOT EXISTS t0(c0 TINYINT(200) ZEROFILL PRIMARY KEY UNIQUE) ;
INSERT IGNORE INTO t0(c0) VALUES(-149547112);
SELECT SUM(t0.c0) FROM t0 WHERE LEAST(t0.c0, "0.95");

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

see the following case:

The MySQL manual clarifies that If the arguments comprise a mix of numbers and strings, they are compared as strings.

https://dev.mysql.com/doc/refman/9.1/en/comparison-operators.html#function_least

3. What did you see instead (Required)

// MySQL 8.4.1
MySQL [test]> select  LEAST(t0.c0, "0.95") from t0;
+----------------------+
| LEAST(t0.c0, "0.95") |
+----------------------+
| 0.95                 |
+----------------------+
1 row in set (0.00 sec)

MySQL [test]> SELECT SUM(t0.c0) FROM t0 WHERE LEAST(t0.c0, "0.95");
+------------+
| SUM(t0.c0) |
+------------+
|          0 |
+------------+
1 row in set (0.00 sec)

// TiDB
mysql> select LEAST(t0.c0, "0.95") from t0;
+----------------------+
| LEAST(t0.c0, "0.95") |
+----------------------+
| 0                    |
+----------------------+
1 row in set (0.04 sec)

mysql> SELECT SUM(t0.c0) FROM t0 WHERE LEAST(t0.c0, "0.95");
+------------+
| SUM(t0.c0) |
+------------+
|       NULL |
+------------+
1 row in set (0.04 sec)

4. What is your TiDB version? (Required)

TiDB v8.5.0

[curry-oss]

/label affects-8.5

[zanmato1984]

First the insertion didn't take effect, as the warning shows:

+---------+------+---------------------------------------------+
| Level   | Code | Message                                     |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'c0' at row 1 |
+---------+------+---------------------------------------------+

so a 0 is actually inserted.

Then, when casted to string in MySQL, a TINYINT(N) will result in a string of length N. So TINYINT(200) 0 is casted to "0000...." (200 digits), which alphabetically follows "0.95", so LEAST(c0, "0.95") evaluates "0.95".

TiDB doesn't actually respect the length of a integer, thus the casting simply emits "0", which alphabetically precedes "0.95", so LEAST(c0, "0.95") evaluates "0".

Adjusting severity to minor.