user: Question: What is the average end year of the player from SWE and a Summer transfer window?
Columns: ['Nat.', 'Name', 'Moving from', 'Type', 'Transfer window', 'Ends', 'Transfer fee', 'Source']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['DNK', 'D. Jensen', 'Youth system', 'Promoted', 'Summer', 2011.0, 'Youth system', 'FCK.dk']
SQL:

assistant: SELECT AVG("Ends") FROM "Table" WHERE "Nat." = 'SWE' AND "Transfer window" = 'Summer';