13.1 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.
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