Which Games have Years at club of 1977, and Goals of 17, and a Debut year smaller than 1977?
CREATE TABLE "1970s" (
  "debut_year" real,
  "player" text,
  "games" real,
  "goals" real,
  "years_at_club" text
);
SELECT AVG("games") FROM "1970s" WHERE "years_at_club"='1977' AND "goals"=17 AND "debut_year"<1977;