How many years where Eichstädt had a number of 939?
CREATE TABLE "subdivisions" (
  "year" real,
  "b_tzow" text,
  "schwante" text,
  "vehlefanz" text,
  "neu_vehlefanz" real,
  "marwitz" text,
  "b_renklau" text,
  "eichst_dt" real
);
SELECT COUNT("year") FROM "subdivisions" WHERE "eichst_dt"=939;