user: Question: What's the first year that Guo Xin featured in women'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: [1999.0, 'Marvin Steve', 'Maja Pohar', 'Dmitry Miznikov Valery Strelcov', 'Natalja Esipenko Natalia Golovkina', 'Valery Strelcov Natalia Golovkina']
SQL:

assistant: SELECT MIN("Year") FROM "Table" WHERE "Women's singles" = 'Guo Xin';