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_name_57 ( tournament VARCHAR )

### Question ###
Which 1997's accompanying 1991 was a when the tournament was the australian open?

### Accurate SQL ###

SELECT 1997 FROM table_name_57 WHERE 1991 = "a" AND tournament = "australian open"