ModSQL
Class Aggregate_Count

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

All Implemented Interfaces:

Aggregate, Function

final class Aggregate_Count

extends AbstractAggregate

Implementation of SQL aggregate function COUNT().

Author:

chris.studholme@utoronto.ca

Field Summary

private long	count Current count.
private boolean	count_all True if we are counting rows, false to count non-null values.

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

(package private)

Aggregate_Count()

Method Summary

void	addParameter(Function item) Adds a value (function) to the list of parameters maintained by this function.
Object	evaluate(boolean aggregate) Evaluate the parameter and update the count.
static Function	forName(String name) Returns a new instance of this class if name is "count".
String	functionName() Returns "COUNT".
int	getMaxResultSize() Returns -1.
int	getSQLType() COUNT always returns BIGINT integers.
void	optimize() Prepare the function for use.
void	reset() Resets the current count to zero.

Methods inherited from class ModSQL.AbstractAggregate

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

Methods inherited from class ModSQL.AbstractFunction

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

evaluate, evaluateOrder, getParameter, getParameterCount

Field Detail

count_all

private boolean count_all

True if we are counting rows, false to count non-null values.

count

private long count

Current count.

Constructor Detail

Aggregate_Count

Aggregate_Count()

Method Detail

forName

public static Function forName(String name)

Returns a new instance of this class if name is "count".

Parameters:

name - name of function to find

Returns:

instance of this class or null if name does not match

addParameter

public void addParameter(Function item)
                  throws SQLException

Adds a value (function) to the list of parameters maintained by this function.

Overrides:

addParameter in class AbstractFunction

Parameters:

item - function to add

Throws:

SQLException - if too many parameters have been added

optimize

public void optimize()
              throws SQLException

Prepare the function for use. COUNT() requires exactly one parameter, unless count_all, in which case no parameters are acceptable. If we are doing COUNT(DISTINCT ...), we require a parameter.

Overrides:

optimize in class AbstractFunction

Throws:

SQLException - if the parameters are invalid

functionName

public String functionName()

Returns "COUNT".

Overrides:

functionName in class AbstractFunction

Returns:

name of function

getSQLType

public int getSQLType()

COUNT always returns BIGINT integers.

Returns:

SQL type of data to be returned

getMaxResultSize

public int getMaxResultSize()

Returns -1.

Returns:

maximum size of String returned or -1 if unknown

reset

public void reset()
           throws SQLException

Resets the current count to zero.

Overrides:

reset in class AbstractAggregate

Throws:

SQLException - if a database error occurs

evaluate

public Object evaluate(boolean aggregate)
                throws SQLException,
                       EndOfTable

Evaluate the parameter and update the count. If aggregate is true, the current count is returned and the parameter is not evaluated. This method returns null if aggregate is false.

Parameters:

aggregate - true to return current count

Returns:

Long object if aggregate is true, null otherwise

Throws:

SQLException - if a database-access error occurs

EndOfTable - if thrown by a parameter