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select yr, mm, cnt, prev, round(100-cnt*100.00/prev, 2) prc from ( select yr, mm, cnt, lag(cnt) over (order by yr, mm) prev from ( select year(creationdate) as yr, month(creationdate)as mm, count(*) as cnt from posts where posttypeid between 1 and 2 group by year(creationdate), month(creationdate) ) as x ) as y where cnt < prev order by yr, mm