The development of areas such as remote and airborne sensing, location based services, and geosensor networks enables the collection of large volumes of spatial data. These datasets necessitate the wide application of spatial databases. Queries on these geo-referenced data often require the aggregation of isolated data points to form spatial clusters and obtain properties of the clusters. However, current SQL standard does not provide an effective way to form and query spatial clusters. In this paper, we aim at introducing Cluster By into spatial databases to allow a broad range of interesting queries to be posted on spatial clusters. We also provide a language construct to specify spatial clustering algorithms. The extension is demonstrated with several motivating examples. Categories and Subject Descriptors H.2.3 [Database Management]: Languages--Query languages; H.2.3 [Database Management]: Database Applications--Data mining; H.2.3 [Database Management]: Database Applications--Spat...