Table: croatian_international_tennis
Columns: year
mens_singles
womens_singles
mens_doubles
womens_doubles
mixed_doubles

Question: How many years did Peter Mikkelsen win the Mens Singles?
SQL: SELECT COUNT("year") FROM croatian_international_tennis WHERE "mens_singles" = 'Peter Mikkelsen'

Question: Who won the Men's Doubles when Karina de Wit won the Women's Singles?
SQL: SELECT "mens_doubles" FROM croatian_international_tennis WHERE "womens_singles" = 'Karina de Wit'

Question: How many Mixed Doubles won when Oliver Pongratz won the Men's Singles?
SQL: SELECT COUNT("mixed_doubles") FROM croatian_international_tennis WHERE "mens_singles" = 'Oliver Pongratz'

Question: Who won the Men's Doubles when Guo Xin won the Women's Singles?
SQL: SELECT "mens_doubles" FROM croatian_international_tennis WHERE "womens_singles" = 'Guo Xin'