What is the year that the oldest church was built in Jostedal? 
CREATE TABLE "churches_in_luster" (
  "parish_prestegjeld" text,
  "sub_parish_sogn" text,
  "church_name" text,
  "year_built" real,
  "location_of_the_church" text
);
SELECT MIN("year_built") FROM "churches_in_luster" WHERE "location_of_the_church"='Jostedal';