EliminateDistinctConstant.java

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

import org.apache.doris.nereids.rules.Rule;
import org.apache.doris.nereids.rules.RuleType;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.plans.LimitPhase;
import org.apache.doris.nereids.trees.plans.logical.LogicalLimit;
import org.apache.doris.nereids.trees.plans.logical.LogicalProject;

/**
 * EliminateDistinctConstant.
 * <p>
 * example sql:
 * <pre>
 * select distinct 1,2,3 from tbl
 *          =>
 * select 1,2,3 from (select 1, 2, 3 from tbl limit 1) as tmp
 *  </pre>
 */
public class EliminateDistinctConstant extends OneAnalysisRuleFactory {
    @Override
    public Rule build() {
        return RuleType.ELIMINATE_DISTINCT_CONSTANT.build(
                logicalProject()
                        .when(LogicalProject::isDistinct)
                        .when(project -> project.getProjects().stream().allMatch(Expression::isConstant))
                        .then(project -> new LogicalProject(project.getProjects(), new LogicalLimit<>(1, 0,
                                LimitPhase.ORIGIN, project.child())))
        );
    }
}