CREATE TABLE table_17427 ("Year" FLOAT, "Mens singles" CLOB, "Womens singles" CLOB, "Mens doubles" CLOB, "Womens doubles" CLOB, "Mixed doubles" CLOB)

Who won the womens singles when Marc Zwiebler won the men's singles?
SELECT "Womens singles" FROM table_17427 WHERE "Mens singles" = 'Marc Zwiebler'
SELECT "Womens singles" FROM "table_17427" WHERE "Mens singles" = 'Marc Zwiebler'