Query to Subtract value of Previous Row from Current Row in SQL Server

Hi SUJAYS,

Refer below sample query, Accordingly to your table data change below query.

SQL

DECLARE @Test AS TABLE([Date] DATETIME,TotalRestOfDay INT)
INSERT INTO @Test VALUES('12-1-2016',10)
INSERT INTO @Test VALUES('12-2-2016',12)
INSERT INTO @Test VALUES('12-3-2016',10)
INSERT INTO @Test VALUES('12-4-2016',11)
INSERT INTO @Test VALUES('12-5-2016',12)
INSERT INTO @Test VALUES('12-6-2016',10)
INSERT INTO @Test VALUES('12-7-2016',11)
INSERT INTO @Test VALUES('12-8-2016',10)
INSERT INTO @Test VALUES('12-9-2016',9)
INSERT INTO @Test VALUES('12-10-2016',10)
INSERT INTO @Test VALUES('12-11-2016',13) 
  
DECLARE @Test1 AS TABLE([Date] DATETIME,TotalRestOfDay INT,Diff INT)
  
DECLARE @Counter INT,@Diff1 INT
SET @Counter = 1
SET @Diff1 = 0

WHILE (@Counter <= (SELECT COUNT(*) FROM @Test))
BEGIN
    DECLARE @Date DATETime,@TotalRestOfDay INT,@Diff INT
  
    SELECT @Date = Date,@TotalRestOfDay = TotalRestOfDay,@Diff = TotalRestOfDay
    FROM (SELECT ROW_NUMBER() OVER( ORDER BY (SELECT 0)) Row_Num,Date,TotalRestOfDay FROM @Test) t 
    WHERE t.Row_Num = @Counter   
	IF(@Counter > 1)
	BEGIN
		INSERT INTO @Test1 (Date,TotalRestOfDay,Diff)
		VALUES (@Date,@TotalRestOfDay,@Diff1 - @Diff)
	END
	ELSE
	BEGIN
		INSERT INTO @Test1 (Date,TotalRestOfDay,Diff)
		VALUES (@Date,@TotalRestOfDay,0)
	END

	SET @Diff1 = @Diff
    SET @Counter = @Counter + 1
    CONTINUE;
END
  
SELECT * FROM @Test1

Output