What is the year that the Gary team with mascot of the Tornado joined?
CREATE TABLE "former_members" (
  "school" text,
  "city" text,
  "mascot" text,
  "county" text,
  "year_joined" real,
  "previous_conference" text,
  "year_left" real,
  "conference_joined" text
);
SELECT MIN("year_joined") FROM "former_members" WHERE "city"='gary' AND "mascot"='tornado';