The following code inserts a new row into a table based on a value in another row but it also allows duplicate data. I want to use NOT EXISTS so that if there is already a row with that value then it won't insert another one, but not sure how to integrate this.

```
INSERT INTO [Grading].[dbo].[tblObservations]
       ([FormID]
       ,[Data]
       ,[UserID]
       ,[DateOfObservation]
       ,[Final]
       ,[ValidTo]
       ,[ID_Grading]
       ,[ID_ObservationKind]
       ,[Created]
       ,[Modified]
       ,[RowVersion])
SELECT [FormID]
  ,'0'
  ,[UserID]
  ,[DateOfObservation]
  ,[Final]
  ,[ValidTo]
  ,[ID_Grading]
  ,40
  ,[Created]
  ,[Modified]
  ,[RowVersion]
  FROM [Grading].[dbo].[tblObservations]
  WHERE [ID_ObservationKind] = 39 AND [Data] = 'No' AND [Final] = 1

```

Any help appreciated.