CREATE TABLE train (Railway_ID VARCHAR2)
CREATE TABLE railway (Builder VARCHAR2, Railway_ID VARCHAR2)

Show the id and builder of the railway that are associated with the most trains.
SELECT T2.Railway_ID, T1.Builder FROM railway AS T1 JOIN train AS T2 ON T1.Railway_ID = T2.Railway_ID GROUP BY T2.Railway_ID ORDER BY COUNT(*) DESC LIMIT 1
SELECT "T2"."Railway_ID", "T1"."Builder" FROM "railway" "T1" JOIN "train" "T2" ON "T1"."Railway_ID" = "T2"."Railway_ID" GROUP BY "T2"."Railway_ID" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY