Microsoft SQL Server 2022的T-SQL新增不少功能，本專題中針對WINDOW子句，以下以Northwind做為範例資料庫，做範例說明。
WINDOW子句是ISO/IEC SQL標準，在視窗函數中，可以命名視窗定義的一部分（或整個視窗），然後在查詢視窗函數的 OVER 子句中使用視窗名稱。以避免重複定義視窗相同的部分，縮短程式碼。
WINDOW子句位置在T-SQL中，SELECT語法的GROUP BY和HAVING子句之間：
SELECT
WHERE
GROUP BY
WINDOW
HAVING
ORDER BY
WINDOW子句語法如下：
WINDOW window_name AS ( [reference_window_name]
[ <window partition clause> ]
[ <window order clause> ]
[ <window frame clause> ] )
以下範例未使用WINDOW子句
SELECT c.CategoryID, c.CategoryName,
p.ProductID, p.ProductName, p.UnitPrice,
SUM(p.UnitPrice) OVER (
PARTITION BY c.CategoryID
ORDER BY p.UnitPrice
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
) AS RunningTotal
FROM dbo.Products p
INNER JOIN dbo.Categories c
ON p.CategoryID = c.CategoryID
執行後的結果：
SELECT c.CategoryID, c.CategoryName,
p.ProductID, p.ProductName, p.UnitPrice,
SUM(p.UnitPrice) OVER
POR
AS RunningTotal
FROM dbo.Products p
INNER JOIN dbo.Categories c
ON p.CategoryID = c.CategoryID
WINDOW
P AS(PARTITION BY c.CategoryID),
PO AS(P ORDER BY p.UnitPrice),
POR AS(PO ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW);
OVER子句中的內容，無法重複利用，常常在撰寫視窗函數時會讓整個T-SQL語法變得紊亂，利用WINDOW子句可以讓這個問題獲得改善，在下一個例子中示範重複使用定義好的WINDOW子句。
SELECT c.CategoryID, c.CategoryName,
p.ProductID, p.ProductName, p.UnitPrice,
SUM(p.UnitPrice) OVER
POR
AS RunningTotal,
AVG(p.UnitPrice) OVER (
PO
ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
AS MovingAverage
FROM dbo.Products p
INNER JOIN dbo.Categories c
ON p.CategoryID = c.CategoryID
WINDOW
P AS(PARTITION BY c.CategoryID),
PO AS(P ORDER BY p.UnitPrice),
POR AS(PO ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW);
可以重複利用先前已定義好的語法，不必再重新將冗長的語法再重複一次，只需要使用定義在WINDOW子句中簡稱P, PO, POR讓整個T-SQL語法可以更簡潔易懂。
執行後的結果：
下面這個例子中：
SELECT e.EmployeeID, e.FirstName,
MONTH(o.OrderDate) AS OrderMonth,
SUM(od.Quantity*od.UnitPrice) AS Total,
SUM(SUM(od.Quantity*od.UnitPrice)) OVER () AS TotalAll,
--總合計
SUM(SUM(od.Quantity*od.UnitPrice)) OVER
P
AS TotalEmployee,
--該月合計
SUM(SUM(od.Quantity*od.UnitPrice)) OVER
PO
AS RunningTotal,
--累計至當月
AVG(SUM(od.Quantity*od.UnitPrice)) OVER
POR
AS MovingAvg
--近三個月平均
FROM dbo.Employees e
INNER JOIN dbo.Orders o
ON e.EmployeeID = o.EmployeeID
INNER JOIN dbo.[Order Details] od
ON o.OrderID = od.OrderID
WHERE YEAR(o.OrderDate) = 1997
GROUP BY e.EmployeeID, e.FirstName, MONTH(o.OrderDate)
WINDOW
P AS (PARTITION BY e.EmployeeID),
PO AS (P ORDER BY MONTH(o.OrderDate)),
POR AS (PO ROWS BETWEEN 2 PRECEDING AND CURRENT ROW);
執行後的結果：
相較於過去的方式，可以有較為簡潔的語法，方便管理維護T-SQL語法。
