Introduction

This chapter covers several topics that relate to basic statistical techniques. For the most part, these recipes build on those described in earlier chapters, such as the summary techniques discussed in Chapter 7. The examples here thus show additional ways to apply the material from those chapters. Broadly speaking, the topics discussed in this chapter include:

• Techniques for data characterization, such as calculating descriptive statistics, generating frequency distributions, counting missing values, and calculating least-squares regressions or correlation coefficients
• Randomization methods, such as how to generate random numbers and apply them to randomization of a set of rows or to selecting individual items randomly from the rows
• Rank assignments

Statistics covers such a large and diverse array of topics that this chapter necessarily only scratches the surface, and simply illustrates a few of the potential areas in which MySQL may be applied to statistical analysis. Note that some statistical measures can be defined in different ways (for example, do you calculate standard deviation based on n degrees of freedom, or n-1?). For that reason, if the definition I use for a given term doesn't match the one you prefer, you'll need to adapt the queries or algorithms shown here to some extent.

You can find scripts related to the examples discussed here in the stats directory of the recipes distribution, and scripts for creating some of the example tables in the tables directory.