instruction: Tags which no longer exists (ordered by number of questions).
response: WITH tagshistory_cte AS (SELECT Id AS phid, REPLACE(value, '>', '') AS TagName FROM PostHistory JOIN LATERAL STRING_SPLIT(Text, '<') WHERE PostHistoryTypeId IN (3, 6, 9) AND LENGTH(value) > 0) SELECT th.TagName, COUNT(DISTINCT ph.PostId) AS "count" FROM tagshistory_cte AS th INNER JOIN PostHistory AS ph ON ph.Id = th.phid WHERE (th.TagName NOT IN (SELECT TagName FROM Tags)) GROUP BY th.TagName ORDER BY COUNT(DISTINCT ph.PostId) DESC