CREATE TABLE table_3953 ("Code" TEXT, "District" TEXT, "Headquarters" TEXT, "Population  ( 2001 Census ) " FLOAT, "Population  ( 2011 Census ) " FLOAT, "Area  ( km\\u00b2 ) " FLOAT, "Density in 2011  ( /km\\u00b2 ) " TEXT)

What's the code of the district with 800.5 people per km2?
SELECT "Code" FROM table_3953 WHERE "Density in 2011 (/km\u00b2)" = '800.5'
SELECT "Code" FROM "table_3953" WHERE "Density in 2011 (/km\u00b2)" = '800.5'