How many people in 1991 have a Village (German) of rupertiberg?
CREATE TABLE "references" (
  "village_german" text,
  "village_slovene" text,
  "number_of_people_1991" real,
  "percent_of_slovenes_1991" text,
  "percent_of_slovenes_1951" text
);
SELECT COUNT("number_of_people_1991") FROM "references" WHERE "village_german"='rupertiberg';