ModSQL
Class Aggregate_Math

java.lang.Object
  |
  +--ModSQL.AbstractFunction
        |
        +--ModSQL.AbstractAggregate
              |
              +--ModSQL.Aggregate_Math

All Implemented Interfaces:

Aggregate, Function

final class Aggregate_Math

extends AbstractAggregate

Implementation of SQL aggregate functions SUM(), AVG() and STDEV(). The return type of each function is function and parameter dependent. AVG() and STDEV() will return type DOUBLE and SUM() will return either type BIGINT or DOUBLE, depending on whether the parameter is an integer or a floating point number, respectively. If there is no parameter, the return type is NULL for all functions. If there are no non-null values to aggregate, SUM() will return 0, but AVG() and STDEV() will return NULL.

Author:

chris.studholme@utoronto.ca

Field Summary

static int	AVG Function is AVG().
private long	count Current count of non-null values.
private int	op Which function are we? One of the constants above.
private int	return_type SQL return type for this function.
static int	STDEV Function is STDEV().
static int	SUM Function is SUM().
private double	sum_double Current sum as a DOUBLE.
private long	sum_long Current sum as a BIGINT.
private double	sum_square Current sum of squares.

Fields inherited from class ModSQL.AbstractAggregate

distinct, distinct_set

Fields inherited from class ModSQL.AbstractFunction

all_constant, constant_non_null, evaluate_order, evaluate_order_array, out_of_order, parameter_constant, parameter_value, parameters, parameters_array

Fields inherited from interface ModSQL.Function

MATCH_BEGINS, MATCH_EQU, MATCH_GT, MATCH_GTE, MATCH_LT, MATCH_LTE, MATCH_NE

Constructor Summary

Aggregate_Math(int op)
Constructor.

Method Summary

Object	evaluate(boolean aggregate) Evaluate parameters and update count and sums.
static Function	forName(String name) Returns a new instance of this class if name is "sum", "avg", or "stdev".
String	functionName() Returns the name of this function for use by toString() method.
int	getMaxResultSize() Returns -1 as these functions never return String objects.
int	getSQLType() Return the SQL type of the value that this function expects to return.
void	optimize() Prepare the function for use.
void	reset() Resets the current count and sums to zero.

Methods inherited from class ModSQL.AbstractAggregate

addDistinctValue, getDistinctSetSize, isAggregate, isConstant, prefixParameters, registerWith, setDistinct

Methods inherited from class ModSQL.AbstractFunction

addParameter, convertToSQLType, evaluate, evaluateConstantParameters, evaluateOrder, evaluateParameters, evaluateParameters, getCompatableType, getObjectSQLType, getParameter, getParameterCount, postfixParameters, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface ModSQL.Function

addParameter, evaluate, evaluateOrder, getParameter, getParameterCount

Field Detail

SUM

public static final int SUM

Function is SUM().

AVG

public static final int AVG

Function is AVG().

STDEV

public static final int STDEV

Function is STDEV().

op

private int op

Which function are we? One of the constants above.

return_type

private int return_type

SQL return type for this function.

count

private long count

Current count of non-null values.

sum_long

private long sum_long

Current sum as a BIGINT.

sum_double

private double sum_double

Current sum as a DOUBLE.

sum_square

private double sum_square

Current sum of squares.

Constructor Detail

Aggregate_Math

public Aggregate_Math(int op)

Constructor.

Parameters:

op - function type

Method Detail

forName

public static Function forName(String name)

Returns a new instance of this class if name is "sum", "avg", or "stdev". The instance is initialized as needed to represent the desired function.

Parameters:

name - name of function to find

Returns:

instance of this class or null if name does not match

optimize

public void optimize()
              throws SQLException

Prepare the function for use. All functions accept at most one parameter and require a parameter if DISTINCT is specified. This method also decides on an appropriate return type.

Overrides:

optimize in class AbstractFunction

Throws:

SQLException - if the parameters are invalid

functionName

public String functionName()

Returns the name of this function for use by toString() method.

Overrides:

functionName in class AbstractFunction

Returns:

name of function

getSQLType

public int getSQLType()
               throws SQLException

Return the SQL type of the value that this function expects to return.

Returns:

SQL type of data to be returned

getMaxResultSize

public int getMaxResultSize()

Returns -1 as these functions never return String objects.

Returns:

maximum size of String returned or -1 if unknown

reset

public void reset()
           throws SQLException

Resets the current count and sums to zero.

Overrides:

reset in class AbstractAggregate

Throws:

SQLException - if a database error occurs

evaluate

public Object evaluate(boolean aggregate)
                throws SQLException,
                       EndOfTable

Evaluate parameters and update count and sums. If aggregate is false, the parameter is evaluated and the count and sums are updated, but this method always returns null. If aggregate is true, the parameter is not evaluated, and the current evaluation of the function is returned.

Parameters:

aggregate - true to return final aggregate value

Returns:

result object

Throws:

SQLException - if a database-access error occurs

EndOfTable - if thrown by a parameter