Name the lowest 2008 for guizhou when 2005 is less than 31
CREATE TABLE "ranking_of_chinese_provinces_by_gdp_per_" (
  "year" text,
  "2010" real,
  "2009" real,
  "2008" real,
  "2005" real,
  "2000" real
);
SELECT MIN("2008") FROM "ranking_of_chinese_provinces_by_gdp_per_" WHERE "year"='guizhou' AND "2005"<31;