What year has a decile more than 6, in the Waikouaiti area?
CREATE TABLE "waitaki_district" (
  "name" text,
  "years" text,
  "gender" text,
  "area" text,
  "authority" text,
  "decile" real,
  "roll" real
);
SELECT "years" FROM "waitaki_district" WHERE "decile">6 AND "area"='waikouaiti';