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Sams Teach Yourself SQL in 10 Minutes, Fourth Edition by Ben Forta

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Lesson 9. Summarizing Data

In this lesson, you will learn what the SQL aggregate functions are and how to use them to summarize table data.

Using Aggregate Functions

It is often necessary to summarize data without actually retrieving it all, and SQL provides special functions for this purpose. Using these functions, SQL queries are often used to retrieve data for analysis and reporting purposes. Examples of this type of retrieval are

• Determining the number of rows in a table (or the number of rows that meet some condition or contain a specific value).

• Obtaining the sum of a set of rows in a table.

• Finding the highest, lowest, and average values in a table column (either for all rows or for specific rows).

In each of these examples, you ...

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