function format incompatible with MySQL for round up

[eurekaka]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

In TiDB:

mysql> select format(1.123456, 4);
+---------------------+
| format(1.123456, 4) |
+---------------------+
| 1.1234              |
+---------------------+
1 row in set (0.00 sec)

2. What did you expect to see?

In MySQL:

mysql> select format(1.123456, 4);
+---------------------+
| format(1.123456, 4) |
+---------------------+
| 1.1235              |
+---------------------+
1 row in set (0.00 sec)

3. What did you see instead?

Different function result regarding round up.

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

mysql> select tidb_version();
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                                    |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v2.1.0-rc.3-347-ga7907ed
Git Commit Hash: a7907ede7a9a740953b0c753b5b2b7add5b55195
Git Branch: master
UTC Build Time: 2018-12-24 11:14:34
GoVersion: go version go1.11.2 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+