AllPostsAndAcceptedAnswersAndEditedUsers.sql

--Use a Where Clause
SELECT		Posts.Title
			,acceptedAnswer.CreationDate
			,Users.DisplayName
FROM		dbo.Posts
LEFT JOIN	dbo.Posts AS acceptedAnswer
	   ON	acceptedAnswer.Id = Posts.AcceptedAnswerId

LEFT JOIN	dbo.Users
		ON	acceptedAnswer.LastEditorUserId = Users.Id
WHERE		Posts.PostTypeId = 1
  AND
			( (	 acceptedAnswer.Id IS NULL AND Users.Id IS NULL)
		   OR (	 acceptedAnswer.Id IS NOT NULL AND Users .Id IS NOT NULL)
			)
      
--Use a nested join
SELECT		Posts.Title
			,acceptedAnswer.CreationDate
			,Users.DisplayName
FROM		dbo.Posts
LEFT JOIN	dbo.Posts AS acceptedAnswer
		INNER	JOIN  dbo.Users
			  ON  acceptedAnswer.LastEditorUserId = Users.Id
	   ON	acceptedAnswer.Id = Posts.AcceptedAnswerId

WHERE		Posts.PostTypeId = 1