ModSQL
Class AbstractAggregate

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

All Implemented Interfaces:

Aggregate, Function

Direct Known Subclasses:

Aggregate_Count, Aggregate_Math, Aggregate_MinMax

public abstract class AbstractAggregate

extends AbstractFunction

implements Aggregate

Abstract implementation of Aggregate to simplify the implementation of real aggregate functions.

Author:

chris.studholme@utoronto.ca

Field Summary

protected boolean	distinct True if the aggregate should eliminate duplicate values before aggregating.
protected HashSet	distinct_set Hash table used to eliminate duplicate values.

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

AbstractAggregate()

Method Summary

boolean	addDistinctValue(Object value) Add a value to the set of distinct values.
int	getDistinctSetSize() Get the size of the set of distinct values.
boolean	isAggregate() Aggregate functions will always return true when isAggregate() is called, unless one of the parameters is an aggregate.
boolean	isConstant() Determine if this function returns a constant value.
String	prefixParameters() Returns "DISTINCT" if distinct was requested, or "*" if the parameter list is empty and optimize() has already been called.
void	registerWith(Object o) This implementation blocks the registerWith() call if the supplied object is of type GroupByList to prevent ColumnValue's that appear in the GROUP BY list from mistakenly being labled as aggregate.
void	reset() This implemenation calls reset() for all parameters and clears the distinct_set hash table.
void	setDistinct() Specify that this aggregate should eliminate duplicate values before aggregating rows.

Methods inherited from class ModSQL.AbstractFunction

addParameter, convertToSQLType, evaluate, evaluateConstantParameters, evaluateOrder, evaluateParameters, evaluateParameters, functionName, getCompatableType, getObjectSQLType, getParameter, getParameterCount, optimize, 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, evaluate, evaluateOrder, getMaxResultSize, getParameter, getParameterCount, getSQLType, optimize

Field Detail

distinct

protected boolean distinct

True if the aggregate should eliminate duplicate values before aggregating.

distinct_set

protected HashSet distinct_set

Hash table used to eliminate duplicate values.

Constructor Detail

AbstractAggregate

public AbstractAggregate()

Method Detail

setDistinct

public void setDistinct()
                 throws SQLException

Specify that this aggregate should eliminate duplicate values before aggregating rows.

Specified by:

setDistinct in interface Aggregate

Throws:

SQLException - if DISTINCT is not allowed

prefixParameters

public String prefixParameters()

Returns "DISTINCT" if distinct was requested, or "*" if the parameter list is empty and optimize() has already been called.

Overrides:

prefixParameters in class AbstractFunction

Returns:

"DISTINCT ", "*", or "" as needed

registerWith

public void registerWith(Object o)
                  throws SQLException

This implementation blocks the registerWith() call if the supplied object is of type GroupByList to prevent ColumnValue's that appear in the GROUP BY list from mistakenly being labled as aggregate. Otherwise, super.registerWith() is used.

Specified by:

registerWith in interface Function

Overrides:

registerWith in class AbstractFunction

Parameters:

o - object to register with

Throws:

SQLException - if an error occurs

isConstant

public boolean isConstant()
                   throws SQLException

Determine if this function returns a constant value. Aggregate functions are rarely constant (even if all of their parameters are constant) so this method always returns false.

Specified by:

isConstant in interface Function

Overrides:

isConstant in class AbstractFunction

Returns:

false

Throws:

SQLException - if an error occurs

isAggregate

public boolean isAggregate()
                    throws SQLException

Aggregate functions will always return true when isAggregate() is called, unless one of the parameters is an aggregate. In this latter case, an exception is thrown as aggregates within aggregates are not allowed in SQL.

Specified by:

isAggregate in interface Function

Overrides:

isAggregate in class AbstractFunction

Returns:

true unless exception

Throws:

SQLException - if any parameters are aggregates

reset

public void reset()
           throws SQLException

This implemenation calls reset() for all parameters and clears the distinct_set hash table. Derived classes should override this method (but still call it) to reset its state.

Specified by:

reset in interface Function

Overrides:

reset in class AbstractFunction

Throws:

SQLException - if an error occurs

addDistinctValue

public boolean addDistinctValue(Object value)

Add a value to the set of distinct values. This method initializes distinct_set if null.

Returns:

true if the value was not already in the distinct set

getDistinctSetSize

public int getDistinctSetSize()

Get the size of the set of distinct values.

Returns:

number of distinct values in hash table