Which 2008 had a 1998 and 2006 that were a when 2009 was sf?
CREATE TABLE "doubles_performance_timeline" (
  "tournament" text,
  "1998" text,
  "1999" text,
  "2000" text,
  "2001" text,
  "2002" text,
  "2003" text,
  "2004" text,
  "2005" text,
  "2006" text,
  "2007" text,
  "2008" text,
  "2009" text,
  "2010" text,
  "2011" text
);
SELECT "2008" FROM "doubles_performance_timeline" WHERE "1998"='a' AND "2009"='sf' AND "2006"='a';