user: ### NOW ANSWER:
Question: When did Mika Heinonen Susanna Dahlberg win mixed doubles?
Columns: ['Year', "Men's singles", "Women's singles", "Men's doubles", "Women's doubles", 'Mixed doubles']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1955.0, 'Lars Palmen', 'Inger Gerkman', 'Lars Palmen Harry Troupp', 'no competition', 'no competition']
SQL:

assistant: SELECT AVG("Year") FROM "Table" WHERE "Mixed doubles" = 'Mika Heinonen Susanna Dahlberg';