In the previous chapters, the data in the result table came directly from the beginning table or was a function of a single row of that table. In this chapter, the data in the result table can summarize the data in an entire column of the beginning table. This is done using a column function. The seven types of column functions provide different ways to summarize the data in a column.
In the next chapter, you will see how to control the level of summarization. In this chapter, the summarization always produces a single row in the result table.