ProjectWithDistinctToAggregate.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.NamedExpression;
import org.apache.doris.nereids.trees.expressions.WindowExpression;
import org.apache.doris.nereids.trees.plans.logical.LogicalAggregate;
import org.apache.doris.nereids.trees.plans.logical.LogicalPlan;
import org.apache.doris.nereids.trees.plans.logical.LogicalProject;
import org.apache.doris.nereids.util.ExpressionUtils;

import com.google.common.collect.ImmutableList;

/**
 * ProjectWithDistinctToAggregate.
 * <p>
 * example sql:
 * <pre>
 * select distinct value from tbl
 *
 * LogicalProject(projects=[distinct value])
 *            |
 * LogicalOlapScan(table=tbl)
 *          =>
 * LogicalAggregate(groupBy=[value], output=[value])
 *           |
 * LogicalOlapScan(table=tbl)
 *  </pre>
 */
public class ProjectWithDistinctToAggregate extends OneAnalysisRuleFactory {
    @Override
    public Rule build() {
        return RuleType.PROJECT_WITH_DISTINCT_TO_AGGREGATE.build(
            logicalProject()
                .when(LogicalProject::isDistinct)
                .whenNot(project -> ExpressionUtils.hasNonWindowAggregateFunction(project.getProjects()))
                .then(this::rewrite)
        );
    }

    private LogicalPlan rewrite(LogicalProject<?> project) {
        boolean hasWindowExpression = false;
        for (NamedExpression expr : project.getProjects()) {
            if (expr.containsType(WindowExpression.class)) {
                hasWindowExpression = true;
                break;
            }
        }
        if (hasWindowExpression) {
            // for distinct, group by = agg output
            // if the project contains window expression, because agg group by cannot
            // contains window function, we need to project them, otherwise CheckAnalysis will fail.
            ImmutableList.Builder<NamedExpression> aggOutput
                    = ImmutableList.builderWithExpectedSize(project.getProjects().size());
            for (NamedExpression output : project.getProjects()) {
                aggOutput.add(output.toSlot());
            }
            return new LogicalAggregate<>(aggOutput.build(), false, project.withDistinct(false));
        } else {
            return new LogicalAggregate<>(project.getProjects(), false, project.child());
        }
    }
}