org.apache.derby.impl.sql.execute

Class CountAggregator

java.lang.Object

org.apache.derby.impl.sql.execute.SystemAggregator

org.apache.derby.impl.sql.execute.CountAggregator

All Implemented Interfaces:

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

public final class CountAggregator
extends SystemAggregator

Aggregator for COUNT()/COUNT(*).

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	isCountStar
private long	value

Constructor Summary

Constructors

Constructor and Description
CountAggregator()

Method Summary

Methods

Modifier and Type	Method and Description
protected void	accumulate(DataValueDescriptor addend)
void	accumulate(DataValueDescriptor addend, java.lang.Object ga) Accumulate for count().
DataValueDescriptor	getResult() Return the result of the aggregation.
int	getTypeFormatId() Get the formatID which corresponds to this class.
boolean	isCountStar()
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 cf, java.lang.String aggregateName, DataTypeDescriptor returnType) 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 org.apache.derby.impl.sql.execute.SystemAggregator

didEliminateNulls, toString

Methods inherited from class java.lang.Object

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

Field Detail

value

private long value

isCountStar

private boolean isCountStar

Constructor Detail

CountAggregator

public CountAggregator()

Method Detail

setup

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

Description copied from interface: ExecAggregator

Set's up the aggregate for processing.

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.

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()

Return the result of the aggregation. Just spit out the running count.

Returns:

the value as a Long

accumulate

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

Accumulate for count(). Toss out all nulls in this kind of count. Increment the count for count(*). Count even the null values.

Specified by:

accumulate in interface ExecAggregator

Overrides:

accumulate in class SystemAggregator

Parameters:

addend - value to be added in

ga - the generic aggregator that is calling me

Throws:

StandardException - on error

See Also:

ExecAggregator.accumulate(org.apache.derby.iapi.types.DataValueDescriptor, java.lang.Object)

accumulate

protected final void accumulate(DataValueDescriptor addend)

Specified by:

accumulate in class SystemAggregator

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

isCountStar

public boolean isCountStar()

writeExternal

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

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.

Specified by:

writeExternal in interface java.io.Externalizable

Overrides:

writeExternal in class SystemAggregator

Throws:

java.io.IOException - thrown on error

readExternal

public final 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 SystemAggregator

Throws:

java.io.IOException - io exception

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