What was the total number of years than had best improved singer (躍進歌手)?
CREATE TABLE "awards_and_nominations" (
  "year" real,
  "award" text,
  "category" text,
  "nomination" text,
  "result" text
);
SELECT SUM("year") FROM "awards_and_nominations" WHERE "category"='best improved singer (躍進歌手)';