Package org.apache.qpid.server.query.engine.parsing.expression.function.aggregation

Class CountExpression<T>

java.lang.Object

org.apache.qpid.server.query.engine.parsing.expression.AbstractExpressionNode<T,R>

org.apache.qpid.server.query.engine.parsing.expression.function.AbstractFunctionExpression<T,R>

org.apache.qpid.server.query.engine.parsing.expression.function.aggregation.AbstractAggregationExpression<T,Number>

org.apache.qpid.server.query.engine.parsing.expression.function.aggregation.CountExpression<T>

Type Parameters:

T - Input parameter type

All Implemented Interfaces:

Function<T,Number>, Expression<T,Number>, ExpressionNode<T,Number>

public class CountExpression<T>
extends AbstractAggregationExpression<T,Number>

The COUNT() function returns the number of items that matches a specified criterion.

Field Summary

Fields inherited from class org.apache.qpid.server.query.engine.parsing.expression.function.AbstractFunctionExpression

_functionName

Fields inherited from class org.apache.qpid.server.query.engine.parsing.expression.AbstractExpressionNode

_metadata

Constructor Summary

Constructors

Constructor	Description
CountExpression(String alias, List<ExpressionNode<T,?>> args)	Constructor initializes children expression list

Method Summary

Modifier and Type	Method	Description
Number	aggregate(List<T> items)	Performs count operation using parameters and the value supplied
CollectorType	getCollectorType()	Returns counting collector type

Methods inherited from class org.apache.qpid.server.query.engine.parsing.expression.function.aggregation.AbstractAggregationExpression

apply, getArguments, getSource, setSelect, setValue

Methods inherited from class org.apache.qpid.server.query.engine.parsing.expression.function.AbstractFunctionExpression

evaluateChild, getFunctionName, getOptionalConstantParameter, getOptionalParameter, getRequiredParameter

Methods inherited from class org.apache.qpid.server.query.engine.parsing.expression.AbstractExpressionNode

containsAggregation, ctx, evaluateChild, getAggregations, getAlias, getChild, getChildren, getParent, isAccessor, isInstantlyEvaluable, setAlias, setParent, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.qpid.server.query.engine.parsing.expression.Expression

andThen

Methods inherited from interface java.util.function.Function

andThen, compose

Constructor Detail

CountExpression

public CountExpression(String alias,
                       List<ExpressionNode<T,?>> args)

Constructor initializes children expression list

Parameters:

alias - Expression alias

args - List of children expressions

Method Detail

getCollectorType

public CollectorType getCollectorType()

Returns counting collector type

Specified by:

getCollectorType in class AbstractAggregationExpression<T,Number>

Returns:

CollectorType instance

aggregate

public Number aggregate(List<T> items)

Performs count operation using parameters and the value supplied

Specified by:

aggregate in class AbstractAggregationExpression<T,Number>

Parameters:

items - Collection to perform aggregation on

Returns:

Aggregated result