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_35318 ( "Player" text, "Attempts" real, "Net yards" real, "Yards per attempt" real, "Touchdowns" real )

### Question ###
How many yards per attempt have net yards greater than 631?

### Accurate SQL ###

SELECT SUM("Yards per attempt") FROM table_35318 WHERE "Net yards" > '631'