SELECT * 
FROM [shared].[Document] D
	LEFT JOIN [shared].[Document] THUMB ON D.[ObjectId]=THUMB.[ObjectId] AND D.[Object]=57 AND THUMB.[Object]=57 AND D.[Id]<>THUMB.[ID]
	AND LEFT(D.[Name], LEN(D.[Name])-CHARINDEX('.', reverse(D.[Name])))=LEFT(THUMB.[Name], LEN(THUMB.[Name])-CHARINDEX('.', reverse(THUMB.[Name])))

WHERE THUMB.[Id] IS NOT NULL AND THUMB.[Name] LIKE '%.png'