Sebastiao Pereira gets out the measuring tape:
How do you calculate the distance between two different points on a sphere using TSQL in SQL Server? In this article, we look at how this can be done to calculate different points on the globe.
Sebastiao first shows the raw calculation, then uses the GEOGRAPHY data type to simplify the job. Note that these are “as the crow flies” distances and not travel distances, as there’s no information on roads.
Also, these are calculations specific to Earth. Which sounds like the setup for a joke, but it’s really not. If you have a smaller sphere (or oblong spheroid, if you will) and you want to calculate the distance, use the GEOMETRY data type instead.