CREATE TABLE table_name_15 (date INT, surface VARCHAR, championship VARCHAR)

What is the earliest Date on a Surface of clay in a Championship in Linz, Austria?
SELECT MIN(date) FROM table_name_15 WHERE surface = "clay" AND championship = "linz, austria"
SELECT MIN("date") FROM "table_name_15" WHERE "championship" = "linz, austria" AND "clay" = "surface"