Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_81 (ends INTEGER, nat VARCHAR, transfer_window VARCHAR)

### Question ###
What is the average end year of the player from swe and a summer transfer window?

### Accurate SQL ###

SELECT AVG(ends) FROM table_name_81 WHERE nat = "swe" AND transfer_window = "summer"