Table: portugal_international_badminton
Columns: year
men_s_singles
women_s_singles
men_s_doubles
women_s_doubles
mixed_doubles

Question: What is the average year with alfredo salazar fina salazar in mixed doubles?
SQL: SELECT AVG("year") FROM portugal_international_badminton WHERE "mixed_doubles" = 'alfredo salazar fina salazar'

Question: Which women's doubles happened after 1987 and a women's single of astrid van der knaap?
SQL: SELECT "women_s_doubles" FROM portugal_international_badminton WHERE "year" > 1987 AND "women_s_singles" = 'astrid van der knaap'