In 1987, what is the Runners-up when Stefan Edberg is Champion?
CREATE TABLE "singles_champions" (
  "year" real,
  "name_of_tournament" text,
  "champions" text,
  "runners_up" text,
  "score" text
);
SELECT "runners_up" FROM "singles_champions" WHERE "champions"='stefan edberg' AND "year"=1987;