CREATE TABLE table_200_33 (id DECIMAL, "district" TEXT, "area size\ ( km2 ) " TEXT, "population" TEXT, "density\ per km2" DECIMAL)

which district has the highest population density ?
SELECT "district" FROM table_200_33 ORDER BY "density\nper km2" DESC LIMIT 1
SELECT "district" FROM "table_200_33" ORDER BY "density\nper km2" DESC NULLS LAST LIMIT 1