Chapter 8
GROUP BY and HAVING
In this chapter we will discuss how to use aggregation, grouping, and the HAVING clause in a SELECT. By using these added features, we can group data of a particular type, filter the output with HAVING, and do combinations of aggregate calculations (such as sums, averages, and counts). We will also take another look at nulls.
Aggregates/Column Functions
As we discussed in Chapter 4, an aggregate (or group) function is one that extracts information — such as a COUNT of rows in a table. We can also find an average, minimum, or maximum for some column by operating on multiple rows. Some examples are:
We can now proceed ...
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