A specialized group of spatial functions that are called spatial predicates can improve query performance. Spatial predicates, such as ST_Overlaps, which compares two polygons to see if they overlap, can be expensive to execute for both time and memory requirements. Therefore, optimization techniques to minimize execution cost are very important. The DB2 query optimizer uses the spatial index to improve query performance when you use the spatial predicates according to the rules described later in this section. For more information about spatial predicates, see Predicate functions. The spatial predicates used to exploit the spatial index are:
For a complete list of all spatial functions and predicates, see Spatial functions for SQL queries.