phoenix-core/src/main/java/org/apache/phoenix/expression/function/CoalesceFunction.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.sql.SQLException;
import java.util.List;

import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.exception.SQLExceptionCode;
import org.apache.phoenix.exception.SQLExceptionInfo;
import org.apache.phoenix.expression.CoerceExpression;
import org.apache.phoenix.expression.Expression;
import org.apache.phoenix.hbase.index.util.ImmutableBytesPtr;
import org.apache.phoenix.parse.FunctionParseNode.Argument;
import org.apache.phoenix.parse.FunctionParseNode.BuiltInFunction;
import org.apache.phoenix.schema.tuple.Tuple;
import org.apache.phoenix.schema.types.PDataType;
import org.apache.phoenix.util.ExpressionUtil;


/**
 *
 * Function used to provide an alternative value when the first argument is null.
 * Usage:
 * COALESCE(expr1,expr2)
 * If expr1 is not null, then it is returned, otherwise expr2 is returned.
 *
 * TODO: better bind parameter type matching, since arg2 must be coercible
 * to arg1. consider allowing a common base type?
 *
 * @since 0.1
 */
@BuiltInFunction(name=CoalesceFunction.NAME, args= {
    @Argument(),
    @Argument()} )
public class CoalesceFunction extends ScalarFunction {
    public static final String NAME = "COALESCE";

    public CoalesceFunction() {
    }

    public CoalesceFunction(List<Expression> children) throws SQLException {
        super(children);

        Expression firstChild = children.get(0);
        Expression secondChild = children.get(1);

        if (ExpressionUtil.isConstant(secondChild)) { // is literal

            ImmutableBytesWritable ptr = new ImmutableBytesPtr();
            secondChild.evaluate(null, ptr);

            if (ptr.getLength()!=0 && !secondChild.getDataType().isCoercibleTo(firstChild.getDataType(), secondChild.getDataType().toObject(ptr))) {
                throw new SQLExceptionInfo.Builder(SQLExceptionCode.TYPE_MISMATCH)
                    .setMessage(getName() + " expected " + firstChild.getDataType() + ", but got " + secondChild.getDataType())
                    .build().buildException();
            }
        } else { // second parameter is expression
            if (!secondChild.getDataType().isCoercibleTo(getDataType())) {
                // cast explicitly
                children.add(1, CoerceExpression.create(secondChild, firstChild.getDataType()));
            }
        }
    }

    @Override
    public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
        boolean evaluated = children.get(0).evaluate(tuple, ptr);
        if (evaluated && ptr.getLength() > 0) {
            return true;
        }
        if (evaluated || tuple.isImmutable()) {
            Expression secondChild = children.get(1);
            if (secondChild.evaluate(tuple, ptr)) {
                // Coerce the type of the second child to the type of the first child
                getDataType().coerceBytes(ptr, secondChild.getDataType(), secondChild.getSortOrder(), getSortOrder());
                return true;
            }
        }
        return false;
    }

    @Override
    public PDataType getDataType() {
        return children.get(0).getDataType();
    }

    @Override
    public Integer getMaxLength() {
        Integer maxLength1 = children.get(0).getMaxLength();
        if (maxLength1 != null) {
            Integer maxLength2 = children.get(1).getMaxLength();
            if (maxLength2 != null) {
                return maxLength1 > maxLength2 ? maxLength1 : maxLength2;
            }
        }
        return null;
    }

    @Override
    public boolean isNullable() {
        return children.get(0).isNullable() && children.get(1).isNullable();
    }

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

    @Override
    public boolean requiresFinalEvaluation() {
        return true;
    }
}