Looping in SQL Server

DECLARE @cnt INT = 1;
WHILE @cnt < (select max(id) FROM [Item])
BEGIN  
 
  update [Stock]
  set [PurchaseQty] = (select [SaleQty] + [BalanceQty] FROM [Stock] where ItemId = @cnt)
  where ItemId = @cnt  
 
  SET @cnt = @cnt + 1;

END;

Pivoting Query

 Actual Table:
Year               Quarter            Amount

1990	1	1.1
1990	2	1.2
1990	3	1.3
1990	4	1.4
1991	1	2.1
1991	2	2.2
1991	3	2.3
1991	4	2.4
1992	4	2.4

Desired Output: 
(Here Q for Quarter)
Year       Q-1       Q-2      Q-3       Q-4
1990        1.1        1.2        1.3        1.4
1991        2.1        2.2        2.3        2.4
1992        0.0        0.0        0.0        2.4
Query:
Use Northwind
GO
CREATE TABLE Pivot
( Year      SMALLINT,
  Quarter   TINYINT,
  Amount      DECIMAL(2,1) )
GO
INSERT INTO Pivot VALUES (1990, 1, 1.1)
INSERT INTO Pivot VALUES (1990, 2, 1.2)
INSERT INTO Pivot VALUES (1990, 3, 1.3)
INSERT INTO Pivot VALUES (1990, 4, 1.4)
INSERT INTO Pivot VALUES (1991, 1, 2.1)
INSERT INTO Pivot VALUES (1991, 2, 2.2)
INSERT INTO Pivot VALUES (1991, 3, 2.3)
INSERT INTO Pivot VALUES (1991, 4, 2.4)
INSERT INTO Pivot VALUES (1992, 4, 2.4)
GO
SELECT * FROM Pivot
GO
SELECT Year,
    SUM(CASE Quarter WHEN 1 THEN Amount ELSE 0 END) AS Q1,
    SUM(CASE Quarter WHEN 2 THEN Amount ELSE 0 END) AS Q2,
    SUM(CASE Quarter WHEN 3 THEN Amount ELSE 0 END) AS Q3,
    SUM(CASE Quarter WHEN 4 THEN Amount ELSE 0 END) AS Q4
FROM Northwind.dbo.Pivot
GROUP BY Year
GO
Another Output:
SELECT P1.*, (P1.Q1 + P1.Q2 + P1.Q3 + P1.Q4) AS YearTotal
FROM (SELECT Year,
             SUM(CASE P.Quarter WHEN 1 THEN P.Amount ELSE 0 END) AS Q1,
             SUM(CASE P.Quarter WHEN 2 THEN P.Amount ELSE 0 END) AS Q2,
             SUM(CASE P.Quarter WHEN 3 THEN P.Amount ELSE 0 END) AS Q3,
             SUM(CASE P.Quarter WHEN 4 THEN P.Amount ELSE 0 END) AS Q4
     FROM Pivot AS P
     GROUP BY P.Year) AS P1
GO