|
||||||||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
An ExecAggregator is the interface that execution uses to an aggregate. System defined aggregates will implement this directly.
The life time of an ExecAggregator is as follows.
Method Summary | |
void |
accumulate(DataValueDescriptor addend,
java.lang.Object ga)
Iteratively accumulates the addend into the aggregator. |
boolean |
didEliminateNulls()
Return true if the aggregation eliminated at least one null from the input data set. |
java.lang.Object |
getResult()
Produces the result to be returned by the query. |
void |
merge(ExecAggregator inputAggregator)
Merges one aggregator into a another aggregator. |
ExecAggregator |
newAggregator()
Return a new initialized copy of this aggregator, any state set by the setup() method of the original Aggregator must be copied into the new aggregator. |
void |
setup(java.lang.String aggregateName)
Set's up the aggregate for processing. |
Methods inherited from interface java.io.Externalizable |
readExternal, writeExternal |
Methods inherited from interface org.apache.derby.iapi.services.io.TypedFormat |
getTypeFormatId |
Method Detail |
public void setup(java.lang.String aggregateName)
public void accumulate(DataValueDescriptor addend, java.lang.Object ga) throws StandardException
addend
- the DataValueDescriptor addend (current input to
the aggregation)ga
- a result set getter
StandardException
- on errorpublic void merge(ExecAggregator inputAggregator) throws StandardException
An example of a merge would be: given two COUNT() aggregators, C1 and C2, a merge of C1 into C2 would set C1.count += C2.count. So, given a CountAggregator with a getCount() method that returns its counts, its merge method might look like this:
public void merge(ExecAggregator inputAggregator) throws StandardException { count += ((CountAccgregator)inputAggregator).getCount(); }
inputAggregator
- the other Aggregator
(input partial aggregate)
StandardException
- on errorpublic java.lang.Object getResult()
public ExecAggregator newAggregator()
public boolean didEliminateNulls()
|
||||||||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |