A user is considered "active" if they have > "threshhold" posts in the given set of tags, where "threshhold" is a parameter that can be set by modifying the textbox below.
Q&A about the site for linguists, teachers and students of the Ukrainian language
select count(distinct Posts.owneruserid)
from posts , PostTags, Tags
where PostTags.PostId = Posts.Id and Tags.Id = PostTags.TagId
and Posts.CreationDate - GETUTCDATE()<60