What is the total number of years Andy Murray was at Wimbledon?
CREATE TABLE "federer_nadal_grand_slam_era" (
  "year" real,
  "australian_open" text,
  "french_open" text,
  "wimbledon" text,
  "us_open" text
);
SELECT COUNT("year") FROM "federer_nadal_grand_slam_era" WHERE "wimbledon"='andy murray';