How many intro dates have the price of 686€?
CREATE TABLE "references" (
  "manufacturer" text,
  "model" text,
  "intro_date" text,
  "interface" text,
  "os" text,
  "price_usd" real,
  "price" text,
  "throughput" text
);
SELECT COUNT("intro_date") FROM "references" WHERE "price"='686€';