Q&A for professional and enthusiast programmers
SELECT DATEPART(year, p.CreationDate) AS Year, DATEPART(month, p.CreationDate) AS Month, COUNT(*) AS count_mysql, COUNT(tj.Id) AS count_json FROM Posts AS p INNER JOIN PostTags AS pm ON p.Id=pm.PostId INNER JOIN Tags AS tm ON pm.TagId=tm.Id AND tm.TagName='mysql' LEFT OUTER JOIN PostTags AS pj ON p.Id=pj.PostId LEFT OUTER JOIN Tags AS tj ON pj.TagId=tj.Id AND tj.TagName='json' WHERE p.PostTypeId=1 GROUP BY DATEPART(year, p.CreationDate), DATEPART(month, p.CreationDate) ORDER BY Year, Month