(Geo|Spatial) - Standard
1 - Opengeospatial
OpenGIS Simple Feature Access SQL is the standard core functionality for spatial/geographical/geometry data, implemented by PostGIS and others.
It basically consists of a GEOMETRY data type (Example with Oracle)and about 150 functions whose names start with
ST_, for example
H2 GIS (A spatial extension of the H2 database) has a good reference. (Look for the functions labeled 'OpenGIS 1.2.1'.)