In this chapter, you learn how to group data so you can summarize subsets of table contents. This involves two new
SELECT statement clauses: the
GROUP BY clause and the
In the last chapter, you learned that the SQL aggregate functions can be used to summarize data. This enables you to count rows, calculate sums and averages, and obtain high and low values without having to retrieve all the data.
All the calculations thus far were 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
SELECT COUNT(*) AS num_prods FROM products WHERE vend_id = 1003;