PushDownProjectThroughLimit.java

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//
//   http://www.apache.org/licenses/LICENSE-2.0
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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.LogicalLimit;
import org.apache.doris.nereids.trees.plans.logical.LogicalProject;

/**
 * <pre>
 * Before:
 *          project
 *             │
 *             ▼
 *           limit
 *             │
 *             ▼
 *          plan node
 *
 * After:
 *
 *           limit
 *             │
 *             ▼
 *          project
 *             │
 *             ▼
 *          plan node
 * </pre>
 */
public class PushDownProjectThroughLimit extends OneRewriteRuleFactory {

    @Override
    public Rule build() {
        return logicalProject(logicalLimit()).thenApply(ctx -> {
            LogicalProject<LogicalLimit<Plan>> logicalProject = ctx.root;
            LogicalLimit<Plan> logicalLimit = logicalProject.child();
            return logicalLimit.withChildren(logicalProject.withChildren(logicalLimit.child()));
        }).toRule(RuleType.PUSH_DOWN_PROJECT_THROUGH_LIMIT);
    }
}