What was the 2008 value when 2012 was Grand Slam Tournaments?
CREATE TABLE "singles_performance_timeline" (
  "tournament" text,
  "2001" text,
  "2002" text,
  "2003" text,
  "2005" text,
  "2006" text,
  "2007" text,
  "2008" text,
  "2009" text,
  "2010" text,
  "2011" text,
  "2012" text
);
SELECT "2008" FROM "singles_performance_timeline" WHERE "2012"='grand slam tournaments';