CREATE TABLE table_name_19 (points VARCHAR(255), wins VARCHAR(255), team VARCHAR(255), class VARCHAR(255), year VARCHAR(255))
How many points numbers had a class of 250cc, a year prior to 1978, Yamaha as a team, and where wins was more than 0?
    
SQL: SELECT COUNT(points) FROM table_name_19 WHERE class = "250cc" AND year < 1978 AND team = "yamaha" AND wins > 0