phoenix-core/src/main/java/org/apache/phoenix/expression/function/FirstValueFunction.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.phoenix.expression.function;

import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.phoenix.expression.Expression;
import org.apache.phoenix.expression.LiteralExpression;
import org.apache.phoenix.expression.aggregator.Aggregator;
import org.apache.phoenix.expression.aggregator.FirstLastValueBaseClientAggregator;
import org.apache.phoenix.expression.aggregator.FirstLastValueServerAggregator;
import org.apache.phoenix.parse.FirstValueAggregateParseNode;
import org.apache.phoenix.parse.FunctionParseNode;
import org.apache.phoenix.schema.types.PBoolean;

/**
 * Built-in function for FIRST_VALUE(<expression>) WITHIN GROUP (ORDER BY <expression> ASC/DESC) aggregate
 * function
 *
 */
@FunctionParseNode.BuiltInFunction(name = FirstValueFunction.NAME, nodeClass = FirstValueAggregateParseNode.class, args = {
    @FunctionParseNode.Argument(),
    @FunctionParseNode.Argument(allowedTypes = { PBoolean.class }, isConstant = true),
    @FunctionParseNode.Argument()})
public class FirstValueFunction extends FirstLastValueBaseFunction {

    public static final String NAME = "FIRST_VALUE";

    public FirstValueFunction() {
    }

    public FirstValueFunction(List<Expression> childExpressions) {
        this(childExpressions, null);
    }

    public FirstValueFunction(List<Expression> childExpressions, CountAggregateFunction delegate) {
        super(childExpressions, delegate);
    }

    @Override
    public Aggregator newServerAggregator(Configuration conf) {
        FirstLastValueServerAggregator aggregator = new FirstLastValueServerAggregator();

        boolean order = (Boolean) ((LiteralExpression) children.get(1)).getValue();
        aggregator.init(children, order, 0);

        return aggregator;
    }

    @Override
    public Aggregator newClientAggregator() {
        FirstLastValueBaseClientAggregator aggregator = new FirstLastValueBaseClientAggregator();
        aggregator.init(0, false);

        return aggregator;
    }

    @Override
    public String getName() {
        return NAME;
    }
}