net.sf.basedb.core.query
Class Aggregations

java.lang.Object
  net.sf.basedb.core.query.Aggregations

public class Aggregations
extends Object

A factory class to create aggregate expressions.

Version:

2.0

Author:

Nicklas

Last modified

$Date: 2009-04-06 14:52:39 +0200 (Mon, 06 Apr 2009) $

Constructor Summary

Aggregations()

Method Summary

static Expression	count(Expression e, boolean distinct) Calculates the number of values for an expression: new expression = COUNT(e)
static Expression	geometricMean(Expression e) Calculates the geometric mean of all values for an expression: new expression = EXP(AVG(LN(e))).
static Expression	max(Expression e) Calculates the maximum value of an expression: new expression = MAX(e)
static Expression	mean(Expression e) Calculates the arithmetic mean of all values for an expression: new expression = AVG(e)
static Expression	min(Expression e) Calculates the minimum value of an expression: new expression = MIN(e)
static Expression	quadraticMean(Expression e) Calculates the quadratic mean, also called Root Mean Square, for an expression: new expression = sqrt(AVG(e*e))
static Expression	sum(Expression e) Calculates the sum of all values of an expression: new expression = SUM(e)

Methods inherited from class java.lang.Object

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

Constructor Detail

Aggregations

public Aggregations()

Method Detail

count

public static Expression count(Expression e,
                               boolean distinct)

Calculates the number of values for an expression: new expression = COUNT(e)

Parameters:

e - The expression to count, or null to count all rows (ie. COUNT(*))

distinct - If only distinct values should be counted

Returns:

The new Expression

geometricMean

public static Expression geometricMean(Expression e)
                                throws InvalidDataException

Calculates the geometric mean of all values for an expression: new expression = EXP(AVG(LN(e))). Note that this method can handle values less then or equal with 0 although the mathematical definition of geometric mean doesn't allow it. This is caused by the way that sql handle null values in aggregated operations. The geometric mean of the numbers [2, -5, 8] is therefor 4 (because ln(-5) is undefined, i.e. null, it is ignored in the avg operation). If you ask a mathematician he would say that the geometic mean is undefined for those numbers.

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidDataException - If the expression is null

Since:

2.4

max

public static Expression max(Expression e)
                      throws InvalidDataException

Calculates the maximum value of an expression: new expression = MAX(e)

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidDataException - If the expression is null

min

public static Expression min(Expression e)
                      throws InvalidDataException

Calculates the minimum value of an expression: new expression = MIN(e)

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidDataException - If the expression is null

mean

public static Expression mean(Expression e)
                       throws InvalidDataException

Calculates the arithmetic mean of all values for an expression: new expression = AVG(e)

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidDataException - If the expression is null

sum

public static Expression sum(Expression e)
                      throws InvalidDataException

Calculates the sum of all values of an expression: new expression = SUM(e)

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidDataException - If the expression is null

quadraticMean

public static Expression quadraticMean(Expression e)

Calculates the quadratic mean, also called Root Mean Square, for an expression: new expression = sqrt(AVG(e*e))

Parameters:

e - The expression to use in the calculation

Returns:

The new Expression

Throws:

InvalidUseOfNullException - If the expression is null

Since:

2.8