Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_21001903_2 ( tour VARCHAR, mixed_doubles VARCHAR, womens_singles VARCHAR )

### Question ###
when mixed doubles is zheng bo ma jin and womens singles is wang yihan, what was the tour?

### Accurate SQL ###

SELECT tour FROM table_21001903_2 WHERE mixed_doubles = "Zheng Bo Ma Jin" AND womens_singles = "Wang Yihan"