Reverting After Impersonation

Kenneth Fisher shows a couple common issues when executing as another user or login:

The problem is that sometimes I’ll forget to revert back.

1	EXECUTE AS LOGIN = 'Doc';

Msg 15406, Level 16, State 1, Line 8
Cannot execute as the server principal because the principal “Doc” does not exist, this type of principal cannot be impersonated, or you do not have permission.

Hey! I know I Doc exists, and I’m sysadmin. How is this not working? Simple enough, I forgot to REVERT. There are two simple options here. I either completely forgot to run it, or I was in the wrong database.

Read the whole thing.