The database server can break up an aggregate computation into several pieces and compute them in parallel. The database server uses the INIT and ITER support functions to compute each piece sequentially. Then the database server uses the COMBINE function to combine the partial results from all the pieces into a single result value. Whether an aggregate is parallel is an optimization decision that is transparent to the user.
Related statements: CREATE FUNCTION and DROP AGGREGATE
For information about how to invoke a user-defined aggregate, see User-Defined Aggregates in the Expression segment.
For a description of the sysaggregates system catalog table that stores data about user-defined aggregates, see the IBM Informix Guide to SQL: Reference.
For a discussion of user-defined aggregates, see IBM Informix User-Defined Routines and Data Types Developer's Guide.