UPDATE On Table Based On Matching Columns

I have 4 rows below in file tblTEST, and I want to be able to transfer the CODE from the MAIN location to the INT location (replacing all existing "A" codes), preceeded by an "I".

ID LOC CODE
-- ----- ------
11 MAIN B
11 INT A
22 MAIN C
22 INT A

I want the result to be:

ID LOC CODE
-- ----- ------
11 MAIN B
11 INT IB
22 MAIN C
22 INT IC

I am stumped as to how to do this - any help or advice would be appreciated.


The only thing I've come up with is:

UPDATE S
SET s.code = B.code
FROM tbltest B
LEFT OUTER JOIN tbltest S ON B.id = S.id
WHERE (S.loc = 'INT')

But when I run it, it says "0 rows affected".