How to change the display encoding of the query result in dbext?

Question

vim

Data in the database (oracle) is stored in cp866 encoding. When using the dbext plugin, the result is returned incorrectly.
The only working (crutch) option, when receiving the result of an sql query, is to change the encoding of the entire editor (set encoding=cp866). Accordingly, this is how you can see the data, but you have to change the encoding back (I have utf-8 on the editor) so that everything works correctly.
Thus, you have to constantly change the encoding, which is not very convenient.
There was a problem with saving data, but it was solved by a similar method described , only I registered my own encoding.
In vim, the configuration settings are specified as follows:

set encoding=utf-8
set fileencodings=utf-8,cp866,cp1251

I am using gVim (Windows 7).
Thank you in advance.