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_15 ( tournament VARCHAR, semi_finalists VARCHAR )

### Question ###
Which Tournament has a Semi finalists of mary pierce elena dementieva?

### Accurate SQL ###

SELECT tournament FROM table_name_15 WHERE semi_finalists = "mary pierce elena dementieva"