CREATE TABLE table_15988037_4 (second_place VARCHAR2, winner VARCHAR2)

Who got second place when the winners were rafa mroczek & aneta piotrowska?
SELECT second_place FROM table_15988037_4 WHERE winner = "Rafał Mroczek & Aneta Piotrowska"
SELECT "second_place" FROM "table_15988037_4" WHERE "Rafał Mroczek & Aneta Piotrowska" = "winner"