Spatial Data Cluster in sql-server ? ( like ST_ClusterWithin in Postgis )
Having looked a the description of ST_ClusterWithin, I believe the geography::Point and STDistance methods are what you're looking for. (See Serge's answer to https://stackoverflow.com/questions/42004474/merge-stored-procedure-and-ctefunction-together-to-get-results-from-reference for an example.)