MergeProjectable.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.ProjectMergeable;

/**
 * this rule aims to merge consecutive project. For example:
 * <pre>
 *   project(a)
 *       |
 *   project(a, b)    ->    oneRow(a)
 *       |
 *   project(a, b, c)
 *       |
 *   oneRow(a, b, c, d)
 * </pre>
 */
public class MergeProjectable extends OneRewriteRuleFactory {

    @Override
    public Rule build() {
        // TODO modify ExtractAndNormalizeWindowExpression to handle nested window functions
        // here we just don't merge two projects if there is any window function
        return logicalProject(any().when(ProjectMergeable.class::isInstance))
                .then(MergeProjectable::mergeProjectable)
                .toRule(RuleType.MERGE_PROJECTS);
    }

    /** merge projectable */
    public static Plan mergeProjectable(LogicalProject<?> project) {
        ProjectMergeable child = (ProjectMergeable) project.child();
        return ProjectMergeable.mergeContinuedProjects(project.getProjects(), child).orElse(project);
    }
}