MySQL Crash Course, 2nd Edition

12

Summarizing Data

In this chapter, 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 MySQL provides special functions for this purpose. You can use these functions in MySQL queries to retrieve data for analysis and reporting purposes. These are some examples of this type of retrieval:

• 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 group 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 ...