CREATE TABLE table_204_712 (id DECIMAL, "rank" DECIMAL, "athlete" TEXT, "nationality" TEXT, "time" TEXT, "notes" TEXT)

which athlete had the fastest time for the 20km ?
SELECT "athlete" FROM table_204_712 ORDER BY "time" LIMIT 1
SELECT "athlete" FROM "table_204_712" ORDER BY "time" NULLS FIRST LIMIT 1