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_31 (surface VARCHAR, opponent VARCHAR)

### Question ###
What is Surface, when Opponent is "Jiří Vaněk"?

### Accurate SQL ###

SELECT surface FROM table_name_31 WHERE opponent = "jiří vaněk"