Aggregation information

Aggregation is performed on rows satisfying criteria that are represented by predicates in an SQL statement.

If an aggregate function executes, one of the following statements appears in db2expln output:

   Aggregation
   Predicate Aggregation
   Partial Aggregation
   Partial Predicate Aggregation
   Hashed Partial Aggregation
   Hashed Partial Predicate Aggregation
   Intermediate Aggregation
   Intermediate Predicate Aggregation
   Final Aggregation
   Final Predicate Aggregation

Predicate aggregation means that the aggregation operation was processed as a predicate when the data was accessed.

The aggregation statement is followed by another statement that identifies the type of aggregate function that was performed:

   Group By
   Column Function(s)
   Single Record

The specific aggregate function can be derived from the original SQL statement. A single record is fetched from an index to satisfy a MIN or MAX operation.

If predicate aggregation has been performed, there is an aggregation completion operation and corresponding output:

   Aggregation Completion
   Partial Aggregation Completion
   Hashed Partial Aggregation Completion
   Intermediate Aggregation Completion
   Final Aggregation Completion