Spatial query to get enclosing radius/polygon of result set Is it possible in SQL to run a query of spatial data, and then just return a single polygon, or a radius, that encloses, aggregates, all of the spatial data that was in that query into one feature?
Yes, using SQL Server's


"Static Aggregate Geometry Methods"
"Static Aggregate Geography Methods"


You essentially have three options


ConvexHull: returns a polygon that essentially wraps the input with a rubber band,
EnvelopeAggregate: returns a bounding box (polygon) that encapsulates the input (box = lines in a cartesian project, arc segments in a 3d/spheroid/geographic projection)
UnionAggregate: takes all of the inputs and composes them into a single complex-polygon


Note: you mention radius, a radius is a buffer over an input in GIS.

If you need more features, you should check out the free PostgreSQL and PostGIS which supports even more GIS functionality.