Controls the choice of algorithms for processing an aggregate.
DBA permissions are not required to set this option. Can be set temporary for an individual connection or for the PUBLIC group. Takes effect immediately.
For aggregation (GROUP BY, DISTINCT, SET functions) within a query, the Sybase IQ optimizer has a choice of several algorithms for processing the aggregate. AGGREGATION_PREFERENCE lets you override the costing decision of the optimizer when choosing the algorithm. the option does not override internal rules that determine whether an algorithm is legal within the query engine.
This option is normally used for internal testing and for manually tuning queries that the optimizer does not handle well. Only experienced DBAs should use it. Inform Sybase Technical Support, if you need to set AGGREGATION_PREFERENCE, as setting this option might mean that a change to the optimizer is necessary.
Value |
Action |
|---|---|
0 |
Let the optimizer choose |
1 |
Prefer aggregation with a sort |
2 |
Prefer aggregation using IQ indexes |
3 |
Prefer aggregation with a hash |
-1 |
Avoid aggregation with a sort |
-2 |
Avoid aggregation using IQ indexes |
-3 |
Avoid aggregation with a hash |