CREATE TABLE "by_county" (
  "province" text,
  "prefecture" text,
  "county" text,
  "tujia_population" real,
  "pct_of_china_s_tujia_population" text
);

Question: Which province has a prefecture of Xiangxi with 0.81% of China's Tujia population?
SQL: SELECT "province" FROM "by_county" WHERE "prefecture"='xiangxi' AND "pct_of_china_s_tujia_population"='0.81%';

Question: Which prefecture is in Hubei province and Enshi county?
SQL: SELECT "prefecture" FROM "by_county" WHERE "province"='hubei' AND "county"='enshi';

Question: What is the sum of Tujia population with the Zhangjiajie prefecture in Sangzhi county?
SQL: SELECT SUM("tujia_population") FROM "by_county" WHERE "prefecture"='zhangjiajie' AND "county"='sangzhi';