How to handle null when passing Chinese characters in json

If nullecho is transmitted in json, it will be normally displayed if it is a letter. if the Chinese character is null, what should I do? My default encoding is gb2312. it is easy to use a conversion function to convert to UTF-8. However, the data retrieved from the database cannot be used. the default encoding of the database is l json, and the Chinese character is transmitted. the display is null.
If echo is a letter, it will be displayed normally. if the Chinese character is null, what should we do? My default encoding is gb2312. it is easy to use a conversion function to convert it to UTF-8. However, the data retrieved from the database will not work. the default encoding in the database is latin1. how should I deal with this problem?

------ Solution --------------------
I also encountered this problem two days ago. I used Wamp 5.0.
Solution:
When the database is created, select utf8_general_ci for the "sorting" option.
When creating various tables, the "sorting" attribute of each record should also be set to utf8_general_ci.

The problem is solved!
------ Solution --------------------
Pick me up
------ Solution --------------------
What is mysql_set_charset () used? I don't understand!