On the problem of Transcoding between fileencoding and encoding in vim

I saw the following introduction in the vim document:

Vim :
-  "fileencoding"  "encoding" 
-  "fileencoding"  "encoding" 
-  "termencoding"  "encoding" 
-  "termencoding"  "encoding" 
-  LC_MESSAGE  "encoding"  (
  gettext)
- Vim   :scriptencoding   "encoding" 
-   viminfo  
  +iconv   "chaconvert" 

but I don"t see who converts to whom, such as: "when reading files, "fileencoding" is different from" encoding"", is encoding converted to fileencoding or fileencoding converted to encoding?

another: will this encoding transform destroy the contents of the file? If the value of fileencoding is not the actual encoding of the file, is this conversion still valid?

Vim
Jun.08,2022
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b30cbc-e291.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b30cbc-e291.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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