Can you tell me the 2010 that has the 2008 of grand slam tournaments?
CREATE TABLE "mixed_doubles_performance_timeline" (
  "tournament" text,
  "2008" text,
  "2009" text,
  "2010" text,
  "2011" text,
  "2012" text,
  "2013" text
);
SELECT "2010" FROM "mixed_doubles_performance_timeline" WHERE "2008"='grand slam tournaments';