Which tournament had a qf in 2011?
CREATE TABLE "mixed_doubles_performance_timeline" (
  "tournament" text,
  "2007" text,
  "2008" text,
  "2009" text,
  "2010" text,
  "2011" text,
  "2012" text,
  "2013" text
);
SELECT "tournament" FROM "mixed_doubles_performance_timeline" WHERE "2011"='qf';