user: ### NOW ANSWER:
Question: What player played women's singles when Marcus Ellis Heather Olver played 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: [2012.0, 'Chou Tien-chen', 'Sashina Vignes Waran', 'Ruud Bosch Koen Ridder', 'Samantha Barning Eefje Muskens', 'Jorrit de Ruiter Samantha Barning']
SQL:

assistant: SELECT "Women's singles" FROM "Table" WHERE "Mixed doubles" = 'Marcus Ellis Heather Olver';