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/*
 * 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.
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package com.hazelcast.org.apache.calcite.rel.rules;

import com.hazelcast.org.apache.calcite.plan.RelOptRuleCall;
import com.hazelcast.org.apache.calcite.plan.RelRule;
import com.hazelcast.org.apache.calcite.rel.core.Aggregate;
import com.hazelcast.org.apache.calcite.rel.core.AggregateCall;
import com.hazelcast.org.apache.calcite.rel.core.Values;
import com.hazelcast.org.apache.calcite.rex.RexBuilder;
import com.hazelcast.org.apache.calcite.rex.RexLiteral;
import com.hazelcast.org.apache.calcite.tools.RelBuilder;
import com.hazelcast.org.apache.calcite.tools.RelBuilderFactory;
import com.hazelcast.org.apache.calcite.util.Util;

import com.hazelcast.com.google.common.collect.ImmutableList;

import org.immutables.value.Value;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

/**
 * Rule that applies {@link Aggregate} to a {@link Values} (currently just an
 * empty {@code Value}s).
 *
 * 

This is still useful because {@link PruneEmptyRules#AGGREGATE_INSTANCE} * doesn't handle {@code Aggregate}, which is in turn because {@code Aggregate} * of empty relations need some special handling: a single row will be * generated, where each column's value depends on the specific aggregate calls * (e.g. COUNT is 0, SUM is NULL). * *

Sample query where this matters: * *

SELECT COUNT(*) FROM s.foo WHERE 1 = 0
* *

This rule only applies to "grand totals", that is, {@code GROUP BY ()}. * Any non-empty {@code GROUP BY} clause will return one row per group key * value, and each group will consist of at least one row. * * @see CoreRules#AGGREGATE_VALUES */ @Value.Enclosing public class AggregateValuesRule extends RelRule implements SubstitutionRule { /** Creates an AggregateValuesRule. */ protected AggregateValuesRule(Config config) { super(config); } @Deprecated // to be removed before 2.0 public AggregateValuesRule(RelBuilderFactory relBuilderFactory) { this(Config.DEFAULT .withRelBuilderFactory(relBuilderFactory) .as(Config.class)); } @Override public void onMatch(RelOptRuleCall call) { final Aggregate aggregate = call.rel(0); final Values values = call.rel(1); Util.discard(values); final RelBuilder relBuilder = call.builder(); final RexBuilder rexBuilder = relBuilder.getRexBuilder(); final List literals = new ArrayList<>(); for (final AggregateCall aggregateCall : aggregate.getAggCallList()) { switch (aggregateCall.getAggregation().getKind()) { case COUNT: case SUM0: literals.add( rexBuilder.makeLiteral(BigDecimal.ZERO, aggregateCall.getType())); break; case MIN: case MAX: case SUM: literals.add(rexBuilder.makeNullLiteral(aggregateCall.getType())); break; default: // Unknown what this aggregate call should do on empty Values. Bail out to be safe. return; } } call.transformTo( relBuilder.values(ImmutableList.of(literals), aggregate.getRowType()) .build()); // New plan is absolutely better than old plan. call.getPlanner().prune(aggregate); } /** Rule configuration. */ @Value.Immutable public interface Config extends RelRule.Config { Config DEFAULT = ImmutableAggregateValuesRule.Config.of() .withOperandFor(Aggregate.class, Values.class); @Override default AggregateValuesRule toRule() { return new AggregateValuesRule(this); } /** Defines an operand tree for the given classes. */ default Config withOperandFor(Class aggregateClass, Class valuesClass) { return withOperandSupplier(b0 -> b0.operand(aggregateClass) .predicate(aggregate -> aggregate.getGroupCount() == 0) .oneInput(b1 -> b1.operand(valuesClass) .predicate(values -> values.getTuples().isEmpty()) .noInputs())) .as(Config.class); } } }





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