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SELECT COUNT(P.Id) AS Num_Posts, SUM(CASE WHEN C.PostId IS NULL THEN 1 ELSE 0 END) AS Posts_NoComments, (SUM(CASE WHEN C.PostId IS NULL THEN 1 ELSE 0 END) / COUNT(*)) * 100 AS Percent_NoComments FROM Posts P LEFT JOIN Comments C ON C.PostId = P.Id