Recently, researches on relational database approaches to sensor networks are being tried. There occur, however, some problems in applying directly the traditional relational database concepts into a sensor network in that every database operation is performed only on the real existing data which are tuples in database relations. The reason is because in a sensor network viewpoint situations under which some operations should be performed on non-existing data may occur frequently. For instance, Can we write a query to get temperature of a spot with no sensor node? Additionally, let us assume a sensor network that two different classes of nodes are scattered in the same area. We cannot get join results to know the relationship between two different classes of sensing values because there might be no nodes at a exact same location. For a solution about the above described problems we propose in this paper new database operators. This new database operators can provide more effective data management and standard interfaces to application programs in sensor networks.