What is the average end year of the player from swe and a summer transfer window?
CREATE TABLE "in" (
  "nat" text,
  "name" text,
  "moving_from" text,
  "type" text,
  "transfer_window" text,
  "ends" real,
  "transfer_fee" text,
  "source" text
);
SELECT AVG("ends") FROM "in" WHERE "nat"='swe' AND "transfer_window"='summer';