What percent of respondents had no opinion on George H.W. Bush?
CREATE TABLE "gallup_poll_2012" (
  "result" text,
  "barack_obama" text,
  "george_h_w_bush" text,
  "ronald_reagan" text,
  "jimmy_carter" text,
  "gerald_ford" text,
  "richard_nixon" text
);
SELECT "george_h_w_bush" FROM "gallup_poll_2012" WHERE "result"='no opinion';