Subqueries

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Three Use Case Examples for SQL Subqueries

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There are many great tutorials on syntax, performance, and keywords for invoking subqueries. However, I wish to discover a tip highlighting selected SQL subquery use cases. Please briefly describe three SQL subquery use case examples. For each use case, cover how a subquery interacts with outer queries and the T-SQL for implementing the use case. Review excerpts from each example to show the value of implementing the use case.

2023-04-14

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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