org.apache.derby.impl.sql.execute

Class VarSAggregator<V extends java.lang.Number>

java.lang.Object

org.apache.derby.impl.sql.execute.VarPAggregator<V>

org.apache.derby.impl.sql.execute.VarSAggregator<V>

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable, Aggregator<V,java.lang.Double,VarPAggregator<V>>

Direct Known Subclasses:

StdDevSAggregator

public class VarSAggregator<V extends java.lang.Number>
extends VarPAggregator<V>

This class implements the SQL Standard VAR_SAMP() aggregator, computing the variance over a sample. It uses the IBM formula described here:

 [ sum(xi2) - sum(xi)2/n ]/(n-1)
 
 where
 
 n is the number of items in the population
 x1 ... xn are the items in the population
 

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.derby.impl.sql.execute.VarPAggregator

VarPAggregator.Sums

Field Summary

Fields

Modifier and Type	Field and Description
private static long	serialVersionUID

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

count, sums

Constructor Summary

Constructors

Constructor and Description
VarSAggregator()

Method Summary

Modifier and Type	Method and Description
protected java.lang.Double	computeVar()

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

accumulate, init, merge, readExternal, terminate, writeExternal

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

Constructor Detail

VarSAggregator

public VarSAggregator()

Method Detail

computeVar

protected java.lang.Double computeVar()

Overrides:

computeVar in class VarPAggregator<V extends java.lang.Number>