What is the average decile with Years of 1–8, and an Area of waipara?
CREATE TABLE "hurunui_district" (
  "name" text,
  "years" text,
  "gender" text,
  "area" text,
  "authority" text,
  "decile" real,
  "roll" real
);
SELECT AVG("decile") FROM "hurunui_district" WHERE "years"='1–8' AND "area"='waipara';