BUG #4916: wish: more statistical functions (median, percentiles etc)

The following bug has been logged online:

Bug reference: 4916
Logged by: Richard Neill
Email address: rn214(at)cam(dot)ac(dot)uk
PostgreSQL version: 8.4
Operating system: Linux
Description: wish: more statistical functions (median, percentiles
etc)
Details:

In addition to the existing aggregate functions (avg, stddev etc), it would
be nice if postgres could return further information. For example, the
quartiles, percentiles, and median.

[mode would also be useful, as an explicit function, though we can get it
easily enough using count(1) order by count desc].

According to google, this has been a wish since at least year 2000 for
various people, but doesn't seem to be implemented.

Thanks - Richard