What is the earliest Date on a Surface of clay in a Championship in Linz, Austria?
CREATE TABLE "singles_titles_16" (
  "outcome" text,
  "date" real,
  "championship" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT MIN("date") FROM "singles_titles_16" WHERE "surface"='clay' AND "championship"='linz, austria';