CREATE TABLE ship (ship_id NUMBER, name CLOB, type CLOB, built_year NUMBER, class CLOB, flag CLOB)
CREATE TABLE captain (captain_id NUMBER, name CLOB, ship_id NUMBER, age CLOB, class CLOB, rank CLOB)

In which year were most of ships built?
SELECT built_year FROM ship GROUP BY built_year ORDER BY COUNT(*) DESC LIMIT 1
SELECT "built_year" FROM "ship" GROUP BY "built_year" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY