org.apache.derby.impl.sql.execute

Class UserDefinedAggregator

java.lang.Object

org.apache.derby.impl.sql.execute.UserDefinedAggregator

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, Formatable, TypedFormat, ExecAggregator

public final class UserDefinedAggregator
extends java.lang.Object
implements ExecAggregator

Aggregator for user-defined aggregates. Wraps the application-supplied implementation of org.apache.derby.agg.Aggregator.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
UserDefinedAggregator() 0-arg constructor for Formatable interface

Method Summary

Modifier and Type	Method and Description
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.
DataValueDescriptor	getResult() Return the result of the aggregation.
int	getTypeFormatId() Get the formatID which corresponds to this class.
void	merge(ExecAggregator addend) 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	readExternal(java.io.ObjectInput in)
void	setup(ClassFactory classFactory, java.lang.String aggregateName, DataTypeDescriptor resultType) Set's up the aggregate for processing.
void	writeExternal(java.io.ObjectOutput out)

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UserDefinedAggregator

public UserDefinedAggregator()

0-arg constructor for Formatable interface

Method Detail

setup

public void setup(ClassFactory classFactory,
                  java.lang.String aggregateName,
                  DataTypeDescriptor resultType)

Description copied from interface: ExecAggregator

Set's up the aggregate for processing.

Specified by:

setup in interface ExecAggregator

Parameters:

classFactory - Database-specific class factory.

aggregateName - For builtin aggregates, this is a SQL aggregate name like MAX. For user-defined aggregates, this is the name of the user-written class which implements org.apache.derby.agg.Aggregator.

resultType - The type returned by the getResult() method.

didEliminateNulls

public boolean didEliminateNulls()

Description copied from interface: ExecAggregator

Return true if the aggregation eliminated at least one null from the input data set.

Specified by:

didEliminateNulls in interface ExecAggregator

accumulate

public void accumulate(DataValueDescriptor addend,
                       java.lang.Object ga)
                throws StandardException

Description copied from interface: ExecAggregator

Iteratively accumulates the addend into the aggregator. Called on each member of the set of values that is being aggregated.

Specified by:

accumulate in interface ExecAggregator

Parameters:

addend - the DataValueDescriptor addend (current input to the aggregation)

ga - a result set getter

Throws:

StandardException - on error

merge

public void merge(ExecAggregator addend)
           throws StandardException

Description copied from interface: ExecAggregator

Merges one aggregator into a another aggregator. Merges two partial aggregates results into a single result. Needed for:

• parallel aggregation
• vector aggregation (GROUP BY)
• distinct aggregates (e.g. MAX(DISTINCT Col))

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();
                } 

Specified by:

merge in interface ExecAggregator

Parameters:

addend - the other Aggregator (input partial aggregate)

Throws:

StandardException - on error

getResult

public DataValueDescriptor getResult()
                              throws StandardException

Return the result of the aggregation. .

Specified by:

getResult in interface ExecAggregator

Returns:

the aggregated result (could be a Java null).

Throws:

StandardException - on error

newAggregator

public ExecAggregator newAggregator()

Description copied from interface: ExecAggregator

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.

Specified by:

newAggregator in interface ExecAggregator

Returns:

ExecAggregator the new aggregator

writeExternal

public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException

Specified by:

writeExternal in interface java.io.Externalizable

Throws:

java.io.IOException - on error

readExternal

public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException

Specified by:

readExternal in interface java.io.Externalizable

Throws:

java.io.IOException - on error

java.lang.ClassNotFoundException

See Also:

Externalizable.readExternal(java.io.ObjectInput)

getTypeFormatId

public int getTypeFormatId()

Get the formatID which corresponds to this class.

Specified by:

getTypeFormatId in interface TypedFormat

Returns:

the formatID of this class