CREATE TABLE table_203_406 (id DECIMAL, "entrant" TEXT, "constructor" TEXT, "chassis" TEXT, "engine" TEXT, "tyre" TEXT, "driver" TEXT, "rounds" TEXT)

what brand has been constructor the most ?
SELECT "constructor" FROM table_203_406 GROUP BY "constructor" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "constructor" FROM "table_203_406" GROUP BY "constructor" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1