What is the population in millions for 2011 where the GDP (nominal) (billions USD) is 4? 
CREATE TABLE "members" (
  "country" text,
  "area_km" text,
  "population_millions_2011" text,
  "gdp_ppp_usd_per_capita" real,
  "gdp_nominal_billions_usd" text,
  "hdi_2011" text
);
SELECT "population_millions_2011" FROM "members" WHERE "gdp_nominal_billions_usd"='4';