What is Assembled, when 2nd Member is "Unknown"?
CREATE TABLE "parliaments_of_king_edward_i" (
  "summoned" text,
  "elected" text,
  "assembled" text,
  "1st_member" text,
  "2nd_member" text
);
SELECT "assembled" FROM "parliaments_of_king_edward_i" WHERE "2nd_member"='unknown';