user: Question: In what mixed doubles did Niels Christian Kaldau play in men's singles?
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: [1986.0, 'Wang Junjie', 'Elinor Allen', 'Ross Glawin Alistair Baker', 'Kristin Magnusdottir Thordis Edwald', 'Alistair Baker Elinor Allen']
SQL:

assistant: SELECT "Mixed doubles" FROM "Table" WHERE "Men's singles" = 'Niels Christian Kaldau';