SQL Fundamentals, Third Edition

Chapter 12. Controlling the Level of Summarization

In chapter 11, we summarized all the data in a column of a table. The result was a single value. In this chapter, we divide the rows of the table into groups, which are nonoverlapping sets of rows. Each group is summarized separately, resulting in a summary value for each of the groups.

At our discretion, we can either summarize a column into a single value or divide it into 100 pieces and summarize each piece. This gives us control over the level of detail we want to see.

Dividing a Table into Groups of Rows		437
12-1	Summary of groups of data within a column	437
12-2	The group by clause	438
12-3	Groups formed on two or more columns	441
12-4	Null groups when there are two or more grouping columns	444
12-5	Summarized ...