The *arithmetic mean* is what you learned in school. However, it is the *harmonic mean* that is often - but not always! - the correct choice when computing an average over a collection of rates.

Median is a *measure of central tendency *useful in describing the typical experience, or the typical case. It's a type of average along with the mean, but less susceptible to skew from outlying values. Median is useful in describing, say, what the typical sale looks like, or what the typical customer is likely to spend.

Oracle Database implements a family of STDDEV functions for computing the standard deviation from the mean. If you think of the mean as beginning to paint a picture of the underlying data, then standard deviation is another brush-stroke toward a fuller picture that will help you draw meaning from the data you're studying.

Read MoreAVG is an aggregate function in SQL to compute the "average" of a set of values. More precisely, it computes the *mean* of those values. And even more precisely, AVG computes what is known as the *arithmetic mean*. But keep reading! Learning about "average" is like uncovering an iceberg. There's more to it than meets the eye.