SELECT AVG(age) FROM syain;
SELECT SUM(age) FROM syain;
SELECT MAX(age) FROM syain;
SELECT MIN(age) FROM syain;
SELECT COUNT(*) FROM syain;

SELECT
	SUM(torihiki.amount)
FROM
	syain,
	tanto,
	torihiki
WHERE
	(syain.id = tanto.id) AND
	(tanto.tid = torihiki.tid);
