Editing Multiple Rows By Their Order Index

Q: How would I go about using / applying the row number of each row in a query to a certain column in the entire query? I've added a screenshot to try and make things more obvious:

Solution 1:

Try this :

;WITH TEST AS 
( 
SELECT *,  
       ROW_NUMBER() OVER (ORDER BY id DESC) AS RowNo 
FROM [UserTable]
) 
UPDATE TEST  
SET  myindex = RowNo