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Discovering SQL: A Hands-On Guide for Beginners by Alex Kriegel

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5

Grouping and Aggregation

Having your data delivered in minute detail works fine until you need to look at the bigger picture. How many books have you accumulated in your library? What is the total cost? How much do you spend on average? These questions, and more, are addressed in SQL with aggregate functions.

We touched on aggregate functions briefly in Chapter 4 as part of the discussion of SQL functions in general and promised to answer a few questions about them; now's the time.

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