MergeOneRowRelationIntoUnion.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.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.NamedExpression;
import org.apache.doris.nereids.trees.expressions.SlotReference;
import org.apache.doris.nereids.trees.plans.Plan;
import org.apache.doris.nereids.trees.plans.logical.LogicalOneRowRelation;
import org.apache.doris.nereids.util.ExpressionUtils;

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

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * merge one row relation into union, for easy to compute physical properties
 */
public class MergeOneRowRelationIntoUnion extends OneRewriteRuleFactory {
    @Override
    public Rule build() {
        return logicalUnion().when(u -> u.children().stream()
                .anyMatch(LogicalOneRowRelation.class::isInstance)).then(u -> {
                    ImmutableList.Builder<List<NamedExpression>> constantExprsList = ImmutableList.builder();
                    List<Plan> newChildren = Lists.newArrayList();
                    ImmutableList.Builder<List<SlotReference>> newChildrenOutputs = ImmutableList.builder();
                    for (int i = 0; i < u.arity(); i++) {
                        Plan child = u.child(i);
                        // if one row relation contains volatile expression which exist multiple times,
                        // don't merge it, later AddProjectForVolatileExpression will handle this one row relation.
                        if (!(child instanceof LogicalOneRowRelation)
                                || ExpressionUtils.containVolatileExpressionExistMultiple(
                                        ((LogicalOneRowRelation) child).getProjects())) {
                            newChildren.add(child);
                            newChildrenOutputs.add(u.getRegularChildOutput(i));
                        } else {
                            ImmutableList.Builder<NamedExpression> constantExprs = new Builder<>();
                            List<NamedExpression> projects = ((LogicalOneRowRelation) child).getProjects();
                            Map<Expression, Expression> replaceMap = new HashMap<>();
                            for (NamedExpression project : projects) {
                                replaceMap.put(project.toSlot(), project);
                            }
                            for (Expression regularChildOutput : u.getRegularChildOutput(i)) {
                                constantExprs.add((NamedExpression) ExpressionUtils.replace(
                                        regularChildOutput, replaceMap));
                            }
                            constantExprsList.add(constantExprs.build());
                        }
                    }
                    // no change
                    if (newChildren.size() == u.arity()) {
                        return u;
                    }
                    return u.withChildrenAndConstExprsList(newChildren,
                            newChildrenOutputs.build(), constantExprsList.build());
                }).toRule(RuleType.MERGE_ONE_ROW_RELATION_INTO_UNION);
    }
}