What is the total decile with an Area of whitianga, and a Roll smaller than 835?
CREATE TABLE "thames_coromandel_district" (
  "name" text,
  "years" text,
  "gender" text,
  "area" text,
  "authority" text,
  "decile" real,
  "roll" real
);
SELECT SUM("decile") FROM "thames_coromandel_district" WHERE "area"='whitianga' AND "roll"<835;