Q&A for Ubuntu users and developers
select top 20 PostTags1.TagId from (select distinct PostTags.TagId, PostTags.PostId from PostTags join Posts on PostTags.PostId = Posts.Id where Posts.CreationDate between '20180101' and '20181231') PostTags1 left join (select distinct PostTags.TagId, PostTags.PostId from PostTags join Posts on PostTags.PostId = Posts.Id where Posts.CreationDate between '20110101' and '20111231') PostTags2 on PostTags1.TagId != PostTags2.TagId