How many different items appear in the enrollment column that joined in 1931, 1949 1?
CREATE TABLE "current_members" (
  "institution" text,
  "location" text,
  "nickname" text,
  "founded" real,
  "type" text,
  "enrollment" real,
  "joined" text
);
SELECT COUNT("enrollment") FROM "current_members" WHERE "joined"='1931, 1949 1';