# What Values Are in the Columns?

The basic charting mechanisms are a good way to see the data, but what do we want to see? The rest of this chapter discusses things of interest when exploring a single table. Although this discussion is in terms of a single table, remember that SQL makes it quite easy to join tables together to make them look like a single table—so the methods apply equally well to multiple tables.

The section starts by investigating frequencies of values, using histograms, for both categorical and numeric values. It then continues to discuss interesting measures (statistics) on columns. Finally, it shows how to gather all these statistics in one rather complex query.

## Histograms

A histogram is a chart—usually a column chart—that shows the distribution of values in a column. For instance, the following query calculates the number of orders and population in each state, answering the question: *What is the distribution of orders by state and how is this...*