Package 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:

Externalizable, Serializable, Formatable, TypedFormat, ExecAggregator

public final class MaxMinAggregator
extends OrderableAggregator

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

See Also:

• OrderableAggregator
• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
private boolean	isMax

Fields inherited from class org.apache.derby.impl.sql.execute.OrderableAggregator

value

Constructor Summary

Constructors

Constructor	Description
MaxMinAggregator()

Method Summary

Modifier and Type	Method	Description
protected void	accumulate(DataValueDescriptor addend)	Accumulate
int	getTypeFormatId()	Get the formatID which corresponds to this class.
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(ObjectInput in)
void	setup(ClassFactory cf, String aggregateName, DataTypeDescriptor returnType)	Set's up the aggregate for processing.
void	writeExternal(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 org.apache.derby.impl.sql.execute.OrderableAggregator

getResult, merge, toString

Methods inherited from class org.apache.derby.impl.sql.execute.SystemAggregator

accumulate, didEliminateNulls

Methods inherited from class java.lang.Object

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

Field Details

isMax

private boolean isMax

Constructor Details

MaxMinAggregator

public MaxMinAggregator()

Method Details

setup

public void setup(ClassFactory cf,
 String aggregateName,
 DataTypeDescriptor returnType)

Description copied from interface: ExecAggregator

Set's up the aggregate for processing.

Specified by:

setup in interface ExecAggregator

Overrides:

setup in class OrderableAggregator

Parameters:

cf - 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.

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

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(ObjectOutput out)
                   throws 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 Externalizable

Overrides:

writeExternal in class OrderableAggregator

Throws:

IOException - on error

See Also:

• Externalizable.writeExternal(java.io.ObjectOutput)

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
ClassNotFoundException

Specified by:

readExternal in interface Externalizable

Overrides:

readExternal in class OrderableAggregator

Throws:

IOException - on error

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