CREATE TABLE table_204_255 (id DECIMAL, "constituency number" DECIMAL, "name" TEXT, "reserved for  ( sc/st/none ) " TEXT, "district" TEXT, "number of electorates  ( 2009 ) " DECIMAL)

which district has the greatest total number of electorates ?
SELECT "district" FROM table_204_255 GROUP BY "district" ORDER BY SUM("number of electorates (2009)") DESC LIMIT 1
SELECT "district" FROM "table_204_255" GROUP BY "district" ORDER BY SUM("number of electorates (2009)") DESC NULLS LAST LIMIT 1