What is the definitive way to determine which user created a tag on a SE site, along with exact date and time of creation?


If you don't mind inaccuracies due to posts that have been deleted, the following query might give you an answer you can work with:

;with taghistory as (
select id
     , creationdate
     , userid as [User Link] 
from posthistory
where posthistorytypeid in (3,6)
and text like '%<##tag##>%'
toptag as (
  select min(creationdate) as [created]
  from taghistory
toprecord as (
  select *
  from taghistory
  where creationdate = (select created from toptag)

select *
from toprecord

It basically relies on the posthistory events for tag editing (3 and 6) and tries to find the tag in the text field (where tagnames are enclosed between < and > ). The earliest date of still visible posts where that tag was added is returned. In theory there could be an earlier record for deleted posts but posthistory doesn't have delete posts and looking at PostsWithDeleted will only tell you if the question had the tag when it was deleted, not when it was added, nor by whom.

For the Haskell tag on Stack Overflow the date returned is 2008-08-19 19:18:41 and the tag was added by Mark Cidade

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