CREATE TABLE table_203_475 (id DECIMAL, "stage" DECIMAL, "date" TEXT, "route" TEXT, "terrain" TEXT, "length" TEXT, "winner" TEXT)

how much longer is the 20th tour de france stage than the 19th ?
SELECT (SELECT "length" FROM table_203_475 WHERE "stage" = 20) - (SELECT "length" FROM table_203_475 WHERE "stage" = 19)
SELECT (SELECT "length" FROM "table_203_475" WHERE "stage" = 20) - (SELECT "length" FROM "table_203_475" WHERE "stage" = 19)