SELECT FeedbackId, ParentFeedbackId, PageId, FeedbackTitle, FeedbackText, FeedbackDate
FROM ReaderFeedback as c
LEFT JOIN (SELECT max(FeedbackId) as MaxFeedbackId FROM ReaderFeedback where ParentFeedbackId IS NOT NULL GROUP BY ParentFeedbackId) as d ON d.MaxFeedbackId = c.FeedbackId
WHERE ParentFeedbackId IS NOT NULL
AND FeedbackText LIKE '%?%' GROUP BY ParentFeedbackId
ORDER BY d.MaxFeedbackId DESC LIMIT 50