Correct use of calendar table to fill gaps

SELECT calendar.datefield
     , revenue.totalrevenue
  FROM calendar
RIGHT JOIN revenue
        ON revenue.date = calendar.datefield
     WHERE (calendar.datefield BETWEEN '2012-01-01' AND '2012-06-30') 
       AND (revenue.productID = 'A'
            OR revenue.totalrevenue = '' 
            OR revenue.totalrevenue IS NULL);

SELECT calendar.datefield
     , revenue.totalrevenue
  FROM calendar
LEFT JOIN revenue
        ON revenue.date = calendar.datefield
     WHERE calendar.datefield BETWEEN '2012-01-01' AND '2012-06-30'
       AND (revenue.productID = 'A' OR revenue.productID IS NULL);

SELECT c.datefield
     , r.totalrevenue
  FROM calendar c
LEFT JOIN revenue r
        ON r.date = c.datefield
     AND r.productID = 'A'
   WHERE c.datefield BETWEEN '2012-01-01' AND '2012-06-30';