Chapter 6. Summarizing and Grouping Data

The preceding chapter described scalar functions, which operate on individual row values. This chapter introduces SQL’s aggregate functions, or set functions, which operate on a group of values to produce a single, summarizing value. You apply an aggregate to a set of rows, which may be:

  • All the rows in a table

  • Only those rows specified by a WHERE clause

  • Those rows created by a GROUP BY clause

No matter how many rows the set contains, an aggregate function returns a single statistic: a sum, minimum, or average, for example.

In this chapter, I’ll also cover the SELECT statement’s GROUP BY clause, which groups rows, and HAVING clause, which filters groups.

Get SQL: Visual QuickStart Guide now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.

Start your free trial