io.trino.sql.planner.iterative.rule.MergeLimitWithTopN 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 io.trino.matching.Capture;
import io.trino.matching.Captures;
import io.trino.matching.Pattern;
import io.trino.sql.planner.iterative.Rule;
import io.trino.sql.planner.plan.LimitNode;
import io.trino.sql.planner.plan.TopNNode;
import static io.trino.matching.Capture.newCapture;
import static io.trino.sql.planner.plan.Patterns.limit;
import static io.trino.sql.planner.plan.Patterns.source;
import static io.trino.sql.planner.plan.Patterns.topN;
/**
* This rule handles both LimitNode with ties and LimitNode without ties.
* In the case of LimitNode with ties, the LimitNode is removed
* if only its row count equals or exceeds TopNNode's row count:
*
* - Limit (5, with ties)
* - TopN (3)
*
* is transformed into:
*
* - TopN (3)
*
* In the case of LimitNode without ties, the LimitNode is removed,
* and the TopNNode's row count is updated to minimum row count
* of both nodes:
*
* - Limit (3)
* - TopN (5)
*
* is transformed into:
*
* - TopN (3)
*
*/
public class MergeLimitWithTopN
implements Rule
{
private static final Capture CHILD = newCapture();
private static final Pattern PATTERN = limit()
.with(source().matching(topN().capturedAs(CHILD)));
@Override
public Pattern getPattern()
{
return PATTERN;
}
@Override
public Result apply(LimitNode parent, Captures captures, Context context)
{
TopNNode child = captures.get(CHILD);
if (parent.isWithTies()) {
if (parent.getCount() < child.getCount()) {
return Result.empty();
}
return Result.ofPlanNode(child);
}
return Result.ofPlanNode(
new TopNNode(
parent.getId(),
child.getSource(),
Math.min(parent.getCount(), child.getCount()),
child.getOrderingScheme(),
parent.isPartial() ? TopNNode.Step.PARTIAL : TopNNode.Step.SINGLE));
}
}