What is the rank for Murphy Oil?
CREATE TABLE "public_companies" (
  "state_rank_by_revenue" real,
  "company_name" text,
  "national_rank" real,
  "revenue_billions_2012_estimate" text,
  "headquarters_city" text,
  "known_for" text
);
SELECT "state_rank_by_revenue" FROM "public_companies" WHERE "company_name"='Murphy Oil';