Is there a command which I can run to do nothing (or very little) which will never error?
I need something for testing porpoises.
A comment does nothing (but your database driver might complain if there is not command at all):
/* Hello, world! */
Unknown PRAGMA statements are ignored, and do not return anything:
PRAGMA testing_porpoises;
If you need a statement that returns an empty result set, you need a SELECT:
SELECT 0 WHERE 0;