Another day, another SQL question:

I need to get quarterly student counts, where a student could appear in multiple quarters, they need to be counted for each quarter.

My first question is simply why does this work...

SELECT MONTH(date) FROM service

but this doesn't...

SELECT QUARTER(date) FROM service

The latter returns an error: Function argument, date, type, or count is invalid

Other than the above, I'm wondering generally how best to tackle this problem. I'm want something like:

SELECT count(person_id), quarter(date);
  FROM service;
  GROUP BY quarter(date)