CREATE TABLE table_203_630 (id DECIMAL, "rank" DECIMAL, "nation" TEXT, "gold" DECIMAL, "silver" DECIMAL, "bronze" DECIMAL, "total" DECIMAL)

which nation earned the most gold medals ?
SELECT "nation" FROM table_203_630 ORDER BY "gold" DESC LIMIT 1
SELECT "nation" FROM "table_203_630" ORDER BY "gold" DESC NULLS LAST LIMIT 1