Guide about date

According to

```
9. [Mandatory] A table must include three columns as following: id, gmt_create and gmt_modified.

Note: id is the primary key, which is unsigned bigint and self-incrementing with step length of 1. The type of gmt_create and gmt_modified should be DATETIME.

```

Can I understand that in Alibaba it is recommended to define the date type as DATETIME? If not, shall we add guide about this? TIMESTAMP or DATETIME is the right choice?

We see that it is mandatory to define gmt_create, gmt_modified, can we understand that when dealing with cross time zone issues you recommend storing the date of gmt time in the database and then converting it to local time zone for display?

No file or test is identified in the issue. First resolve whether the guide should recommend DATETIME or TIMESTAMP and how UTC values should be handled across time zones; done means the guideline contains an unambiguous recommendation and timezone guidance.

Written by the indexing model from the issue text.