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SQL Server execution-plans-3 book cover

Free eBook: SQL Server Execution Plans, Third Edition

If a query is performing poorly, and you can't understand why, then that query's execution plan will tell you not only what data set is coming back, but also what SQL Server did, and in what order, to get that data. It will reveal how the data was retrieved, and from which tables and indexes, what types of joins were used, at what point filtering, sorting and aggregation occurred, and a whole lot more. These details will often highlight the likely source of any problem.

2020-12-23 (first published: )

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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