Precision loss when casting time to string

[zanmato1984]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

select cast(date_add(cast('00:00:00' as time), interval 1.1 second) as char);

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

MySQL 8.0:

+-----------------------------------------------------------------------+
| cast(date_add(cast('00:00:00' as time), interval 1.1 second) as char) |
+-----------------------------------------------------------------------+
| 00:00:01.1                                                            |
+-----------------------------------------------------------------------+

3. What did you see instead (Required)

TiDB:

+-----------------------------------------------------------------------+
| cast(date_add(cast('00:00:00' as time), interval 1.1 second) as char) |
+-----------------------------------------------------------------------+
| 00:00:01                                                              |
+-----------------------------------------------------------------------+

4. What is your TiDB version? (Required)

+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v6.0.0
Edition: Community
Git Commit Hash: 36a9810441ca0e496cbd22064af274b3be771081
Git Branch: heads/refs/tags/v6.0.0
UTC Build Time: 2022-03-31 10:33:28
GoVersion: go1.18
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+