आपको अपनी शामिल होने की शर्तों को सबक्वेरी के अंदर ले जाना होगा
SELECT tour_date AS "Departure Date", site_name "Site Name"
FROM (
SELECT res_id,tour_date,site_name, (res_partcost +NVL(RES_GEARCOST,0)) as "total_cost"
FROM reservation,site,tour
WHERE reservation.tour_id = tour.tour_id
AND tour.site_id = site.site_id ) Res1
WHERE Res1.total_cost > 230 // this will not be displayed in a result
GROUP BY tour_date, site_name;