Table:
text: Bitburger Open
Previous winners
Previous winners
Year_ Mens_singles Womens_singles Mens_doubles Womens_doubles Mixed_doubles
2001 Niels Christian Kaldau Pi Hongyan Michael Søgaard Michael Lamp Neli Boteva Elena Nozdran Chris Bruil Lotte Bruil-Jonathans
2002 Chen Gang Pi Hongyan Simon Archer Flandy Limpele Mia Audina Lotte Bruil-Jonathans Nathan Robertson Gail Emms
2003 Dicky Palyama Xu Huaiwen Michał Łogosz Robert Mateusiak Nicole Grether Juliane Schenk Frederik Bergström Johanna Persson
2004 Niels Christian Kaldau Xu Huaiwen Simon Archer Anthony Clark Kamila Augustyn Nadieżda Kostiuczyk Rasmus Mangor Andersen Britta Andersen
2005 Kasper Ødum Xu Huaiwen Tony Gunawan Halim Haryanto Nicole Grether Juliane Schenk Vladislav Druzhchenko Johanna Persson
2006 Ronald Susilo Xu Huaiwen Michał Łogosz Robert Mateusiak Jiang Yanmei Li Yujia Robert Mateusiak Nadieżda Kostiuczyk

Question: How often did Niels Christian Kaldau and Pi Hongyan win the men's singles and women's singles at the Bitburger Open in the same year?