CREATE TABLE table_204_420 (id DECIMAL, "month" TEXT, "song" TEXT, "artist" TEXT, "aggregate points" DECIMAL, "total downloads" DECIMAL, "year-end chart" DECIMAL)

which song has the most downloads ?
SELECT "song" FROM table_204_420 ORDER BY "total downloads" DESC LIMIT 1
SELECT "song" FROM "table_204_420" ORDER BY "total downloads" DESC NULLS LAST LIMIT 1