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

What is the year in which most ships were 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 NULLS LAST LIMIT 1