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_2665085_1 ( length__ft_ VARCHAR, speed__mph_ VARCHAR )

### Question ###
What is the length of the coaster with the unknown speed

### Accurate SQL ###

SELECT length__ft_ FROM table_2665085_1 WHERE speed__mph_ = "unknown"