Suppose I’m halfway through running an import, and instead of running
SELECT COUNT(*) FROM table_being_imported
I hit ctrl+R, type table_being_im and hit return, only to find to my horror that I’ve just issued
DELETE FROM table_being_imported
Oops. So I hit ctrl+C and get told:
Ctrl-C -- sending "KILL QUERY 627" to server ...
Ctrl-C -- query aborted.
ERROR 1317 (70100): Query execution was interrupted
Would it have deleted any of the rows? Just hypothetically, of course…
hypothetically,… some of those rows are now gone.
Not that this is the time to mention it, but this is why Transactional queries are best when dealing with business-critical data.