When the surface is clay, and the tournament of barcelona what is the score?
CREATE TABLE "singles_18_12_6" (
  "outcome" text,
  "date" text,
  "tournament" text,
  "surface" text,
  "opponent" text,
  "score" text
);
SELECT "score" FROM "singles_18_12_6" WHERE "surface"='clay' AND "tournament"='barcelona';