RemoveRedundantDistinctLimit.java

/*
 * Licensed 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 com.facebook.presto.sql.planner.iterative.rule;

import com.facebook.presto.matching.Captures;
import com.facebook.presto.matching.Pattern;
import com.facebook.presto.spi.plan.DistinctLimitNode;
import com.facebook.presto.sql.planner.iterative.GroupReference;
import com.facebook.presto.sql.planner.iterative.Rule;

import static com.google.common.base.Preconditions.checkArgument;

public class RemoveRedundantDistinctLimit
        implements Rule<DistinctLimitNode>
{
    private static final Pattern<DistinctLimitNode> PATTERN = Pattern.typeOf(DistinctLimitNode.class)
            .matching(RemoveRedundantDistinctLimit::singleRowInput);

    private static boolean singleRowInput(DistinctLimitNode node)
    {
        return (((GroupReference) node.getSource()).getLogicalProperties().isPresent() &&
                ((GroupReference) node.getSource()).getLogicalProperties().get().isAtMostSingleRow());
    }

    @Override
    public Pattern<DistinctLimitNode> getPattern()
    {
        return PATTERN;
    }

    @Override
    public Result apply(DistinctLimitNode node, Captures captures, Context context)
    {
        checkArgument(!node.getHashVariable().isPresent(), "HashSymbol should be empty");
        return Result.ofPlanNode(node.getSource());
    }
}