Obtenga los valores de los últimos 6 meses en mysql

Para MYSQL:puede usar date_add :

 SELECT * FROM ratepersqft 
WHERE date < Now() and date > DATE_ADD(Now(), INTERVAL- 6 MONTH);

Para SQL Server:, dateadd :

  SELECT * FROM ratepersqft 
 WHERE date < Now() and date > DATEADD(Month, -6, Now());

http://www.sqlfiddle.com/#!2/1f8029/48

DEMOSTRACIÓN DE SQLFIDDLE

SELECT *
FROM ratepersqft 
WHERE date_format(date,'%Y-%m') < 
                     date_format(now(),'%Y-%m')
and date_format(date,'%Y-%m') >= 
                     date_format(now() - interval 6 month,'%Y-%m')
order by date desc;