instruction: stack overflow 2019 top tags.
response: SELECT t.TagName, COUNT(*) AS cnt FROM PostTags AS pt LEFT JOIN (SELECT Id FROM Posts WHERE YEAR(CreationDate) = 2019 AND NOT Tags IS NULL) AS p ON pt.PostId = p.Id LEFT JOIN Tags AS t ON pt.TagId = t.Id WHERE NOT pt.TagId IS NULL AND NOT p.Id IS NULL GROUP BY t.TagName ORDER BY cnt DESC