Which series had a release on 1939-07-15 with the 8863 production number?
CREATE TABLE "1939" (
  "title" text,
  "series" text,
  "director" text,
  "production_num" text,
  "release_date" text
);
SELECT "series" FROM "1939" WHERE "release_date"='1939-07-15' AND "production_num"='8863';