Скачать или смотреть T-SQL Tutorial - Aggregate Window Functions Performance

Learn how to measure and optimise aggregate window functions in this T-SQL Tutorial. In the video I show how the version of SQL Server impacts aggregate window functions and how we can make queries that use window functions faster.

If you are not familiar with NTILE, feel free to check out my video on that here:    • SQL Tutorial - How to use NTILE in SQL Server  

You can also watch all my videos on Window Functions within my playlist:    • Window Functions  

If you wish to follow along with the video, you can use the SQL Scripts below:

-- check if table exists
IF OBJECT_ID(N'dbo.Orders', N'U') IS NOT NULL
DROP TABLE dbo.Orders;

-- create table
CREATE TABLE dbo.Orders
(
OrderId BIGINT IDENTITY(1, 1)
CONSTRAINT PK_Orders_OrderID PRIMARY KEY (OrderId),
CustomerId BIGINT,
Amount DECIMAL(6, 2)
);

-- set variables
DECLARE
@Customers BIGINT = 1000,
@NumRows BIGINT = 1000000

;
WITH
L0 AS (SELECT 1 AS N UNION ALL SELECT 1),
L1 AS (SELECT 1 AS N FROM L0 AS A CROSS JOIN L0 AS B),
L2 AS (SELECT 1 AS N FROM L1 AS A CROSS JOIN L1 AS B),
L3 AS (SELECT 1 AS N FROM L2 AS A CROSS JOIN L2 AS B),
L4 AS (SELECT 1 AS N FROM L3 AS A CROSS JOIN L3 AS B),
L5 AS (SELECT 1 AS N FROM L4 AS A CROSS JOIN L4 AS B)

INSERT INTO dbo.Orders (CustomerId, Amount)
SELECT
NTILE(@Customers) OVER(ORDER BY (SELECT NULL)) AS CustomerId,
CAST(ABS(CHECKSUM(NEWID())) / 1000000.00 AS DECIMAL(6, 2)) AS Amount
FROM
(
SELECT TOP(@NumRows)
N
FROM L5
) AS D;

-- aggregate window function
SET STATISTICS TIME ON;
SET STATISTICS IO ON;

SELECT
CustomerId,
Amount,
CAST((Amount * 100) / SUM(Amount) OVER() AS DECIMAL(8, 6)) AS PctofTotal,
CAST((Amount * 100) / SUM(Amount) OVER(PARTITION BY CustomerId) AS DECIMAL(8, 6)) AS PctofCustTotal
FROM dbo.Orders;

SET STATISTICS TIME OFF;
SET STATISTICS IO OFF;

SET STATISTICS TIME ON;
SET STATISTICS IO ON;

-- using derived tables
SELECT
A.CustomerId,
A.Amount,
CAST((A.Amount * 100) / Total AS DECIMAL(8, 6)) AS PctofTotal,
CAST((A.Amount * 100) / CustTotal AS DECIMAL(8, 6)) AS PctofCustTotal
FROM dbo.Orders AS A
INNER JOIN
(
SELECT
CustomerId,
SUM(Amount) AS CustTotal
FROM dbo.Orders
GROUP BY CustomerId
) AS B
ON A.CustomerId = B.CustomerId
CROSS JOIN
(
SELECT
SUM(Amount) AS Total
FROM dbo.Orders
) AS C

SET STATISTICS TIME OFF;
SET STATISTICS IO OFF;