CREATE TABLE table_203_581 (id DECIMAL, "club" TEXT, "chinese" TEXT, "city" TEXT, "home stadium" TEXT, "capacity" DECIMAL, "average attendance" DECIMAL)

what is the average attendance for all stadiums ?
SELECT "average attendance" FROM table_203_581 WHERE agg = 1
SELECT "average attendance" FROM "table_203_581" WHERE "agg" = 1