io.trino.sql.planner.iterative.rule.RemoveRedundantTopN Maven / Gradle / Ivy
/*
* 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 io.trino.sql.planner.iterative.rule;
import com.google.common.collect.ImmutableList;
import io.trino.matching.Captures;
import io.trino.matching.Pattern;
import io.trino.sql.planner.iterative.Rule;
import io.trino.sql.planner.optimizations.Cardinality;
import io.trino.sql.planner.plan.SortNode;
import io.trino.sql.planner.plan.TopNNode;
import io.trino.sql.planner.plan.ValuesNode;
import static io.trino.sql.planner.optimizations.QueryCardinalityUtil.extractCardinality;
import static io.trino.sql.planner.plan.Patterns.topN;
/**
* Replace TopN node
* 1. With a Sort node when the subplan is guaranteed to produce fewer rows than N
* 2. With its source when the subplan produces only one row
* 3. With a empty ValuesNode when N is 0
*/
public class RemoveRedundantTopN
implements Rule
{
private static final Pattern PATTERN = topN();
@Override
public Pattern getPattern()
{
return PATTERN;
}
@Override
public Result apply(TopNNode node, Captures captures, Context context)
{
if (node.getCount() == 0) {
return Result.ofPlanNode(new ValuesNode(node.getId(), node.getOutputSymbols(), ImmutableList.of()));
}
Cardinality sourceCardinality = extractCardinality(node.getSource(), context.getLookup());
if (sourceCardinality.isScalar()) {
return Result.ofPlanNode(node.getSource());
}
if (sourceCardinality.isAtMost(node.getCount())) {
return Result.ofPlanNode(new SortNode(context.getIdAllocator().getNextId(), node.getSource(), node.getOrderingScheme(), false));
}
return Result.empty();
}
}