When I execute a simple statement in phpMyAdmin like
SELECT * FROM a
where \"a\" has 500\'000 rows, it gives me a time of a few milliseconds on
Besides splash21's answer, it is a good idea to use SQL_NO_CACHE when testing for execution time. This makes sure that you are looking at the real time to do the query, not just grabbing a cached result.
SELECT SQL_NO_CACHE * FROM a