Table: croatian_international
Columns: year
men_s_singles
women_s_singles
men_s_doubles
women_s_doubles
mixed_doubles

Question: Give the earliest year that featured Pi Hongyan on women's singles.
SQL: SELECT MIN("year") FROM croatian_international WHERE "women_s_singles" = 'pi hongyan'

Question: What's the first year that Guo Xin featured in women's singles?
SQL: SELECT MIN("year") FROM croatian_international WHERE "women_s_singles" = 'guo xin'