user: Question: Who was the U21 Mens winner when Mike Marsden was the mixed restricted winner and Claire Nelson was the U21 Womens winner? 
Columns: ['Date/Location', 'Mens singles', 'Womens Singles', 'U21 Mens', 'U21 Womens', 'Mixed Restricted', 'Mixed Veteran']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['July 2010 Doncaster', 'Liam Pitchford', 'Kelly Sibley', 'Alim Hirji', 'Karina Le Fevre', 'Will Bayley', 'Abdul Wuraola']
SQL:

assistant: SELECT "U21 Mens" FROM "Table" WHERE "Mixed Restricted" = 'Mike Marsden' AND "U21 Womens" = 'Claire Nelson';