SELECT DAYNAME(dateadded) DAY, COUNT(*) COUNT
FROM `products`
WHERE (`dateadded` BETWEEN DATE_SUB(CURDATE(), INTERVAL 7 DAY) AND CURDATE() && site_url = 'mysite.com')
GROUP BY DAY(dateadded)

SELECT DAYNAME(d.FullDate) DAY, COUNT(*) COUNT
FROM dates d
LEFT OUTER JOIN products p ON d.FullDate = DATE(p.dateadded)
    AND p.site_url = 'mysite.com'
WHERE d.FullDate BETWEEN DATE_SUB(CURDATE(), INTERVAL 7 DAY) AND CURDATE()
GROUP BY d.FullDate