LimitSortToTopN.java

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package org.apache.doris.nereids.rules.rewrite;

import org.apache.doris.nereids.rules.Rule;
import org.apache.doris.nereids.rules.RuleType;
import org.apache.doris.nereids.trees.plans.Plan;
import org.apache.doris.nereids.trees.plans.logical.LogicalProject;
import org.apache.doris.nereids.trees.plans.logical.LogicalSort;
import org.apache.doris.nereids.trees.plans.logical.LogicalTopN;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;

import java.util.List;

/**
 * rule to eliminate limit node by replace to other nodes.
 */
public class LimitSortToTopN implements RewriteRuleFactory {
    @Override
    public List<Rule> buildRules() {
        return ImmutableList.of(
                // limit -> sort ==> topN
                logicalLimit(logicalSort())
                        .then(limit -> {
                            LogicalSort<Plan> sort = limit.child();
                            return new LogicalTopN<>(sort.getOrderKeys(),
                                    limit.getLimit(),
                                    limit.getOffset(),
                                    sort.child(0));
                        }).toRule(RuleType.LIMIT_SORT_TO_TOP_N),
                // limit -> proj -> sort ==> proj -> topN
                logicalLimit(logicalProject(logicalSort()))
                        .then(limit -> {
                            LogicalProject<LogicalSort<Plan>> project = limit.child();
                            LogicalSort<Plan> sort = limit.child().child();
                            LogicalTopN<Plan> topN = new LogicalTopN<>(sort.getOrderKeys(),
                                    limit.getLimit(),
                                    limit.getOffset(),
                                    sort.child(0));
                            return project.withChildren(Lists.newArrayList(topN));
                        }).toRule(RuleType.LIMIT_SORT_TO_TOP_N)
        );
    }
}