SimplifyAggGroupBy.java

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

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.Slot;
import org.apache.doris.nereids.util.Utils;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableSet;

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

/**
 * Remove duplicated aggregate grouping slots. For example
 * <p>
 * GROUP BY ClientIP, ClientIP
 * -->
 * GROUP BY ClientIP
 *
 * <p>Only bare slots can be simplified safely. Derived expressions may lose information through
 * overflow, rounding or truncation, so replacing them with their input slot requires a complete
 * injectivity proof that is not available here.</p>
 */
public class SimplifyAggGroupBy extends OneRewriteRuleFactory {
    @Override
    public Rule build() {
        return logicalAggregate()
                .when(agg -> agg.getGroupByExpressions().size() > 1
                        && agg.getGroupByExpressions().stream().allMatch(SimplifyAggGroupBy::canExtractSlot))
                .then(agg -> {
                    List<Expression> groupByExpressions = agg.getGroupByExpressions();
                    ImmutableSet.Builder<Expression> inputSlots
                            = ImmutableSet.builderWithExpectedSize(groupByExpressions.size());
                    for (Expression groupByExpression : groupByExpressions) {
                        inputSlots.addAll(groupByExpression.getInputSlots());
                    }
                    Set<Expression> slots = inputSlots.build();
                    if (slots.size() != 1) {
                        return null;
                    }
                    return agg.withGroupByAndOutput(Utils.fastToImmutableList(slots), agg.getOutputExpressions());
                })
                .toRule(RuleType.SIMPLIFY_AGG_GROUP_BY);
    }

    @VisibleForTesting
    protected static boolean canExtractSlot(Expression expr) {
        return expr instanceof Slot;
    }

}