What is the earliest year of disaffiliation of a CHCH-TV station, licensed in Hamilton, Ontario?
CREATE TABLE "owned_and_operated" (
  "city_of_license_market" text,
  "station" text,
  "channel_tv_rf" text,
  "year_of_affiliation" real,
  "year_of_disaffiliation" real
);
SELECT MIN("year_of_disaffiliation") FROM "owned_and_operated" WHERE "city_of_license_market"='hamilton, ontario';