List the smallest possible spoilt vote with the sør-trøndelag constituency.
CREATE TABLE "by_constituency" (
  "constituency" text,
  "electorate" real,
  "s_spoilt_vote" real,
  "total_poll_pct" text,
  "for_pct" text,
  "against_pct" text
);
SELECT MIN("s_spoilt_vote") FROM "by_constituency" WHERE "constituency"='Sør-Trøndelag';