I am trying to pull a list of all users who have commented on an answer and tie it back to their User profile, if one exists. However, not all Comments table records have a UserId associated with them in the Stack Exchange Data Explorer result set. Those that do not have a UserId, have a UserDisplayName field instead. What I am curious about is how the User table information is related to the UserDisplayName field. Are these users who have not created an account on Stack Exchange? If they later create an account, is there a way to tie them back together?

I am aware that there is not an ability to ask new questions without creating an account based on this link [https://stackoverflow.com/help/why-register](https://www.stackoverflow.com/help/why-register), but I am curious if there is a way / how to tie back the anon users that answer questions or comment on posts.

To contextualize why I need this, I am interested in exploring the influence of users with the answers on stack exchange using comments for academic research.

Here is the query I am running on SEDE

```
CREATE TABLE #questions (
QuestionId INT)

CREATE TABLE #answers (
AnswerId INT
,questionId INT)

INSERT #questions
SELECT DISTINCT TOP 1000 Posts.Id
FROM Posts
WHERE PostTypeId = 1


INSERT #answers
SELECT DISTINCT 
	Posts.Id
    ,q.questionId
FROM #questions q
INNER JOIN Posts
	ON Posts.ParentID = q.QuestionId
		AND Posts.PostTypeId = 2


SELECT 'https://stackoverflow.com/questions/' + CAST(a.questionId AS CHAR(20))
	SO_Link_Question
	,'https://stackoverflow.com/questions/' + CAST(a.answerId AS CHAR(20))
	SO_Link_Answer
	,UserId
    ,UserDisplayName
FROM Comments c
INNER JOIN #answers a
	ON a.AnswerId = c.PostId
ORDER BY a.questionID, a.answerId
```