IF OBJECT_ID ('dbo.folder_sizes') IS NOT NULL
  DROP TABLE dbo.folder_sizes
GO
CREATE TABLE 
  dbo.folder_sizes
(
  id INT NOT NULL IDENTITY,
  root_name VARCHAR (2000) NOT NULL,
  folder_name VARCHAR (200) NOT NULL,
  size INT,
  logged_at DATETIME DEFAULT GETDATE ()
)
GO

IF OBJECT_ID ('dbo.v_folder_size_changes') IS NOT NULL 
  DROP VIEW dbo.v_folder_size_changes
GO
CREATE VIEW
  dbo.v_folder_size_changes
AS SELECT
  fsi.root_name,
  fsi.folder_name,
  changes.size_change
FROM
  dbo.folder_sizes AS fsi
JOIN
(
  SELECT
    fsi.id,
    size_change = fsi.size - ISNULL ((
      SELECT TOP 1 fsi1.size 
      FROM dbo.folder_sizes AS fsi1 
      WHERE fsi1.folder_name = fsi.folder_name 
      AND fsi1.logged_at < fsi.logged_at
      ORDER BY fsi1.logged_at DESC
    ), 0)
  FROM
    dbo.folder_sizes AS fsi
) AS changes ON
  changes.id = fsi.id
WHERE
  changes.size_change <> 0
GO