PushProjectIntoUnion.java

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// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
//
//   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.rules.expression.ExpressionRewriteContext;
import org.apache.doris.nereids.rules.expression.rules.FoldConstantRule;
import org.apache.doris.nereids.trees.expressions.Alias;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.NamedExpression;
import org.apache.doris.nereids.trees.expressions.Slot;
import org.apache.doris.nereids.trees.expressions.SlotReference;
import org.apache.doris.nereids.trees.plans.algebra.SetOperation.Qualifier;
import org.apache.doris.nereids.trees.plans.logical.LogicalProject;
import org.apache.doris.nereids.trees.plans.logical.LogicalUnion;
import org.apache.doris.nereids.util.ExpressionUtils;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;

import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * Project(Union) -> Union, if union with all qualifier and without children.
 */
public class PushProjectIntoUnion extends OneRewriteRuleFactory {
    @Override
    public Rule build() {
        return logicalProject(logicalUnion())
                .when(this::canPushProjectIntoUnion
        ).thenApply(ctx -> {
            LogicalProject<LogicalUnion> p = ctx.root;
            ExpressionRewriteContext expressionRewriteContext = new ExpressionRewriteContext(ctx.cascadesContext);
            LogicalUnion union = p.child();
            ImmutableList.Builder<List<NamedExpression>> newConstExprs = ImmutableList.builder();
            for (List<NamedExpression> constExprs : union.getConstantExprsList()) {
                Map<Expression, Expression> replaceMap = Maps.newHashMap();
                Map<Expression, NamedExpression> replaceRootMap = Maps.newHashMap();
                for (int i = 0; i < constExprs.size(); i++) {
                    NamedExpression ne = constExprs.get(i);
                    if (ne instanceof Alias) {
                        replaceMap.put(union.getOutput().get(i), ((Alias) ne).child());
                    } else {
                        replaceMap.put(union.getOutput().get(i), ne);
                    }
                    replaceRootMap.put(union.getOutput().get(i), ne);
                }
                ImmutableList.Builder<NamedExpression> newProjections = ImmutableList.builder();
                for (NamedExpression old : p.getProjects()) {
                    if (old instanceof SlotReference) {
                        newProjections.add((NamedExpression) FoldConstantRule.evaluate(replaceRootMap.get(old),
                                expressionRewriteContext));
                    } else {
                        newProjections.add((NamedExpression) FoldConstantRule.evaluate(
                                ExpressionUtils.replaceNameExpression(old, replaceMap), expressionRewriteContext));
                    }
                }
                newConstExprs.add(newProjections.build());
            }
            return p.child().withNewOutputsChildrenAndConstExprsList(ImmutableList.copyOf(p.getOutput()),
                    ImmutableList.of(), ImmutableList.of(), newConstExprs.build());
        }).toRule(RuleType.PUSH_PROJECT_INTO_UNION);
    }

    private boolean canPushProjectIntoUnion(LogicalProject<LogicalUnion> project) {
        LogicalUnion union = project.child();
        if (union.getQualifier() != Qualifier.ALL || union.arity() != 0) {
            return false;
        }
        for (List<NamedExpression> constExprs : union.getConstantExprsList()) {
            Set<Slot> uniqueFunctionSlots = Sets.newHashSet();
            for (int i = 0; i < constExprs.size(); i++) {
                NamedExpression ne = constExprs.get(i);
                if (ne.containsUniqueFunction()) {
                    uniqueFunctionSlots.add(union.getOutput().get(i));
                }
            }
            if (uniqueFunctionSlots.isEmpty()) {
                continue;
            }
            Set<Slot> counterSet = Sets.newHashSet();
            // for a union slot which contains unique function, if it exists in project multiple times,
            // then don't push project into union,  otherwise the unique function will be copy multiple times.
            // e.g. `select a as b, a as c from (select random() as a union all select 2 as a)`
            // if push down the project, then random() will be evaluated twice:  `random() as b, random() as c`
            for (NamedExpression ne : project.getProjects()) {
                if (ne.anyMatch(expr -> expr instanceof Slot
                        && uniqueFunctionSlots.contains(expr) && !counterSet.add((Slot) expr))) {
                    return false;
                }
            }
        }

        return true;
    }
}