org.apache.derby.impl.sql.execute
Class MaxMinAggregator

java.lang.Object
  org.apache.derby.impl.sql.execute.SystemAggregator
      org.apache.derby.impl.sql.execute.OrderableAggregator
          org.apache.derby.impl.sql.execute.MaxMinAggregator

All Implemented Interfaces:

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

public final class MaxMinAggregator

extends OrderableAggregator

Aggregator for MAX()/MIN(). Defers most of its work to OrderableAggregator.

Author:

jamie

See Also:

OrderableAggregator, Serialized Form

Field Summary

private boolean	isMax
protected DataValueDescriptor	value

Constructor Summary

MaxMinAggregator()

Method Summary

protected void	accumulate(DataValueDescriptor addend) Accumulate
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 operations that we have been performing.
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(java.lang.String aggregateName) Set's up the aggregate for processing.
void	writeExternal(java.io.ObjectOutput out) Although we are not expected to be persistent per se, we may be written out by the sorter temporarily.

Methods inherited from class java.lang.Object

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

Field Detail

isMax

private boolean isMax

value

protected DataValueDescriptor value

Constructor Detail

MaxMinAggregator

public MaxMinAggregator()

Method Detail

setup

public void setup(java.lang.String aggregateName)

Description copied from interface: ExecAggregator

Set's up the aggregate for processing.

Specified by:

setup in interface ExecAggregator

Overrides:

setup in class OrderableAggregator

accumulate

protected void accumulate(DataValueDescriptor addend)
                   throws StandardException

Accumulate

Specified by:

accumulate in class SystemAggregator

Parameters:

addend - value to be added in

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.

Returns:

ExecAggregator the new aggregator

writeExternal

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

Description copied from class: OrderableAggregator

Although we are not expected to be persistent per se, we may be written out by the sorter temporarily. So we need to be able to write ourselves out and read ourselves back in. We rely on formatable to handle situations where value is null.

Why would we be called to write ourselves out if we are null? For scalar aggregates, we don't bother setting up the aggregator since we only need a single row. So for a scalar aggregate that needs to go to disk, the aggregator might be null.

Specified by:

writeExternal in interface java.io.Externalizable

Overrides:

writeExternal in class OrderableAggregator

Throws:

java.io.IOException - on error

See Also:

Externalizable.writeExternal(java.io.ObjectOutput)

readExternal

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

Specified by:

readExternal in interface java.io.Externalizable

Overrides:

readExternal in class OrderableAggregator

Throws:

java.io.IOException - on error

java.lang.ClassNotFoundException - on error

See Also:

Externalizable.readExternal(java.io.ObjectInput)

getTypeFormatId

public int getTypeFormatId()

Get the formatID which corresponds to this class.

Returns:

the formatID of this class

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();
                } 

Parameters:

addend - the other Aggregator (input partial aggregate)

Throws:

StandardException - on error

See Also:

ExecAggregator.merge(org.apache.derby.iapi.sql.execute.ExecAggregator)

getResult

public DataValueDescriptor getResult()
                              throws StandardException

Return the result of the operations that we have been performing. Returns a DataValueDescriptor.

Returns:

the result as a DataValueDescriptor

Throws:

StandardException - on error

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