window functions

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Understanding SQL Server PARTITION BY with Examples

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Introduction When developers first learn SQL aggregation, they usually start with the GROUP BY clause. It works well for summary reports because it combines multiple rows into a single result for each group. For example, you can calculate total sales per region or average salary per department. The limitation of GROUP BY appears when you […]

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2026-06-05

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SQLServerCentral Article

SQL Window Functions Series: NTILE()

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Unlock the power of SQL's NTILE function with our latest deep-dive article. Learn to segment your data effectively into quantiles for more nuanced analysis, discover common pitfalls and their solutions, and optimize your queries for peak performance.

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2024-02-03 (first published: )

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SQLServerCentral Article

SQL Window Functions Series: LAG() and LEAD()

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Dive deep into the powerful SQL window functions, LAG() and LEAD(). Explore their intricacies, discover real-world examples, and avoid common pitfalls.

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2023-12-11

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The Empty Aggregate

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Question of the Day

The Empty Aggregate

I have this table in a SQL Server 2025 database:

CREATE TABLE [dbo].[CustomerOrder]
(
[OrderID] [int] NULL,
[CustomerID] [int] NULL,
[total] [money] NULL
) ON [PRIMARY]
GO
What is returned from this code? (answers are for the sum and then the count)
SELECT SUM(total) AS sum,
       COUNT(total) AS count
FROM dbo.CustomerOrder;



See possible answers