Select row from one table and insert into another tables field as XML / JSON in one statement?

I am looking to select a row from one table, collecting the result as XML or JSON and inserting it into another tables field all in one statement without having to handle anything in PHP.

I wonder if I can harness the power of the CLI functionality where you can add a -X to when logging in to retrieve any data returned in XML format?

mysql -u mysql_user -p password -X

Thanks in advance,

Ash.

Additional -

Just to add, this one query not being run from the command line, I mean running it from PHP but not having to handle the data etc in PHP. Thanks again.