Result of function ROUND is different from MySQL

[SunRunAway]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

SELECT ROUND( 'hello', -7787 ) ;

2. What did you expect to see?

mysql> SELECT ROUND( 'hello', -7787 ) ;
+-------------------------+
| ROUND( 'hello', -7787 ) |
+-------------------------+
|                     NaN |
+-------------------------+
1 row in set, 1 warning (0.00 sec)

3. What did you see instead?

mysql> SELECT ROUND( 'hello', -7787 ) ;
+-------------------------+
| ROUND( 'hello', -7787 ) |
+-------------------------+
|                       0 |
+-------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'hello' |
+---------+------+-------------------------------------------+
1 row in set (0.00 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   8c20289

[wjhuang2016]

In MySQL 8.0.15:

mysql> SELECT ROUND( 'hello', -7787 ) ;
+-------------------------+
| ROUND( 'hello', -7787 ) |
+-------------------------+
|                       0 |
+-------------------------+
1 row in set, 1 warning (0.01 sec)

mysql> show warnings;
+---------+------+-------------------------------------------+
| Level   | Code | Message                                   |
+---------+------+-------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'hello' |
+---------+------+-------------------------------------------+
1 row in set (0.00 sec)

[ghost]

It looks like TiDB uses the MySQL 8.0 behavior here (with correct error code and message). Functions are not explicitly documented in the docs yet, but until it is known to affect a user this should be categorized as a compatibility issue and not a bug.

It is not expected to specify decimals (i.e. ROUND(number, decimals)) as a negative value.

[wjhuang2016]

It looks like TiDB uses the MySQL 8.0 behavior here (with correct error code and message). Functions are not explicitly documented in the docs yet, but until it is known to affect a user this should be categorized as a compatibility issue and not a bug.

It is not expected to specify decimals (i.e. ROUND(number, decimals)) as a negative value.

@SunRunAway @nullnotnil Can we close this issue?

[ghost]

Yes, I think it is acceptable to close as "won't fix". We can review if there are requests to the counter.