CREATE TABLE city (city VARCHAR2, city_id VARCHAR2)
CREATE TABLE hosting_city (host_city VARCHAR2)

Which city has hosted the most events?
SELECT T1.city FROM city AS T1 JOIN hosting_city AS T2 ON T1.city_id = T2.host_city GROUP BY T2.host_city ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T1"."city" FROM "city" "T1" JOIN "hosting_city" "T2" ON "T1"."city_id" = "T2"."host_city" GROUP BY "T2"."host_city" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY