MySQL Crash Course, 2nd Edition

13

Grouping Data

In this chapter, you’ll learn how to group data so you can summarize subsets of table contents. Grouping data involves two SELECT statement clauses that you haven’t learned about yet: the GROUP BY clause and the HAVING clause.

Understanding Data Grouping

In the previous chapter, you learned that the SQL aggregate functions can be used to summarize data. By using those functions, you can count rows, calculate sums and averages, and obtain high and low values without having to retrieve all the data.

All the calculations thus far have been performed on all the data in a table or on data that matched a specific WHERE clause. As a reminder, the following example returns the number of products offered by vendor 1003:

Input

SELECT ...