ケース#:トロントで働いて市職員を選択
SELECT
last_name,job_id,e.department_id,department_name
FROM
employees AS e,departments AS d,locations AS l
WHERE
e.`department_id`=d.`department_id`
AND
d.`location_id`=l.`location_id`
AND
l.city='Toronto'
#ケース、各国の国民数で部署の数を照会するには、2より大きい
SELECT
country_id ,COUNT(*)
FROM
locations AS l,departments AS d
WHERE
l.`location_id`=d.`location_id`
GROUP BY
country_id
HAVING
COUNT(*) >2;