percent deleted

SQL

WITH deleted AS (
  SELECT COUNT(ar_rev_id) AS Del, DATE_FORMAT(ar_timestamp,'%Y-%m') AS MONTH
  FROM archive
  WHERE ar_parent_id=0
  GROUP BY MONTH
  ORDER BY MONTH DESC)
  
  ,created AS (
  SELECT COUNT(page_title) AS cre, DATE_FORMAT(rev_timestamp,'%Y-%m') AS creMONTH
  FROM page
    JOIN revision ON revision.rev_page=page.page_id
  WHERE revision.rev_parent_id=0
  GROUP BY creMONTH DESC)
  
SELECT (100.0*(deleted.Del/created.cre)), Del, cre, MONTH
FROM deleted
JOIN created ON deleted.MONTH=created.creMONTH
GROUP BY MONTH
ORDER BY MONTH DESC
SQL

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