Which province has a prefecture of Xiangxi with 0.81% of China's Tujia population?
CREATE TABLE "by_county" (
  "province" text,
  "prefecture" text,
  "county" text,
  "tujia_population" real,
  "pct_of_china_s_tujia_population" text
);
SELECT "province" FROM "by_county" WHERE "prefecture"='xiangxi' AND "pct_of_china_s_tujia_population"='0.81%';