Which Social Democratic Party has a Green smaller than 0?
CREATE TABLE "summary_of_election_results_1973_2003" (
  "election" real,
  "labour" real,
  "conservative" real,
  "liberal" real,
  "social_democratic_party" real,
  "social_and_liberal_democrats_liberal_democrats" real,
  "independent" real,
  "green" real,
  "other" text,
  "control" text
);
SELECT AVG("social_democratic_party") FROM "summary_of_election_results_1973_2003" WHERE "green"<0;